ART. XXVIII.—PALEONTOLOGICAL PAPERS NO. 6: DESCRIPTIONS OF NEW SPECIES OF INVERTEBRATE FOSSILS FROM THE LARAMIE GROUP.

BY C. A. WHITE, M. D.

The fossils described in this paper were collected by the writer (unless otherwise stated in connection with the description) from the strata of the Laramie Group, during the season of 1877, in Colorado, Wyoming, and Utah. Many other associated species were also collected, but only the hitherto undescribed forms are noticed in this paper.

Of the numerous invertebrate forms hitherto collected from the strata of this great group, except some insect remains (to be described by Mr. S. H. Scudder), and a few unstudied Ostracoid Crustaceans, all are molluscan.

CONCHIFERA.

Genus VOLSELLA Scopoli.

Subgenus BRACHYDONTES Swainson.

Volsella (Brachydontes) regularis (n. sp.).

Shell arcuate-subovate in marginal outline; valves moderately convex; upper margin more or less strongly arched from beak to rear; thence with a continuous but stronger curve to the postero-basal margin, which is somewhat abruptly rounded to the gently concave base; front moderately narrow, slightly projecting beyond the beaks, and abruptly rounded to the base; beaks depressed, scarcely perceptible as such, and nearly but not quite terminal; hinge-margin short, nearly straight; umbonal slope somewhat prominent, but conspicuous only by increasing the apparent concavity of the basal part of the shell. Surface marked by numerous, rather coarse, radiating lines, or small costæ, which increase in size toward the free margins of the shell. These costæ have generally a somewhat crenulated aspect, due in part to small sinuosities in their course, and in part to being frequently crossed by lines and undulations of growth; denticles or crenulations of the short front margin distinct.

Length of the type-specimen 36 millimeters; breadth at the widest part 18 millimeters; but several less perfect examples obtained at dif ferent localities indicate a much larger size, the largest of which must have had a length of 63 centimeters.

Position and locality.-Laramie Group. The type-specimen is from the Valley of Crow Creek, Northern Colorado, 15 miles above the confluence of that creek with South Platte River. Other examples are from Cañon Park, Valley of Yampa River; Danforth Hills, near White River Indian agency, Colorado; and Rock Springs Station, Union Pa cific Railroad, Wyoming.

Volsella (Brachydontes) laticostata (sp. nov.).

Shell transversely elongate, arcuate-subelliptical; upper border broadly and almost regularly arched; posterior border somewhat abruptly but continuously rounded from the upper border to the base, which latter border is gently concave along its middle portion; front abruptly rounded, beaks inconspicuous, situated near the front; hinge-line short, nearly straight, not forming an angle with the remainder of the upper border; denticles, or crenulations of the anterior border, distinct. Surface marked by the usual distinct lines of growth, and also by fine radiating costæ, which are obsolete along the whole length of the median portion of the shell, and are more distinct upon and near the dorsal border than elsewhere.

Length 5 centimeters; greatest width 19 millimeters.

This species differs conspicuously from the preceding one, which is from the same formation, in its greater proportionate length, the straighter and less crenulate character of its costa, and their absence or obsolescence upon the median portion of the shell.

Position and locality.-Laramie Group, about 400 feet from its base; Danforth Hills, near White River Indian agency, Colorado.

Genus NUCULANA Link.

Nuculana inclara (sp. nov.).

Shell small, elongate-subovate in marginal outline, gradually narrowing behind the beaks. Beaks not prominent, situated about one-third of the full length of the shell from the front; valves only moderately convex, even in the anterior and umbonal regions, and without distinct umbonal ridges. Basal margin broadly semi-elliptical; anterior margin regularly rounded from the cardinal margin to the base; postero-basal margin sloping upward to the posterior margin, which is sharply rounded to the cardinal margin; the latter margin slightly arched, or the anterior and posterior portions of it forming a very slight angle with each other; denticles minute, numerous, 12 to 15 or more in front of the beak and a greater number behind it.

The few examples discovered being only casts, the true character of the surface is not known, but it appears to have been marked with only the usual concentric lines of growth. Character of the pallial line unknown.

Length 11 millimeters; height from base to beaks 5 millimeters. No

examples larger than this were discovered, but it is possible that those obtained are under full adult size.

Position and locality.-Laramie Group, about 400 feet above its base; Danforth Hills, near White River Indian agency, Northwestern Colorado. Genus ANODONTA Cuvier.

Anodonta parallela (sp. nov.).

Shell transversely much elongate, oblong or semi-elliptical in marginal outline; valves gently convex, apparently a little more so near the front than elsewhere; beaks situated about two-sevenths the length of the shell from the front, depressed, the elevation of the umbonal region being hardly perceptible; hinge-line long; the whole dorsal border nearly straight; both anterior and posterior borders regularly rounded; that of the posterior being a little more abruptly rounded than the front; base nearly straight, or very slightly emarginate along or a little in front of the middle. Test thin; surface smooth or marked only by the ordinary lines of growth and one or two faint ridges running from the beaks to the postero-dorsal margin.

Length 62 millimeters; breadth 20 millimeters.

The extraordinary length of this shell compared with its width is an unusual feature in this genus; but all the other characteristics of the species, so far as they can be observed on the specimens yet discovered, indicate it to be a true Anodonta, and its immediate associates are also all fresh-water shells. Only two examples have been discovered, both imperfect; but together they show all the essential characteristics of the species. Notwithstanding its unusually elongate form, the character of the test and its edentate hinge apparently leave no doubt as to its generic character as here indicated.

Position and locality.-Laramie Group; Valley of Crow Creek, Northern Colorado, about 10 miles above the confluence of the creek with South Platte River.

Genus UNIO Retzius.

Unio goniambonatus (sp. nov.).

Shell of medium size, transversely elongated, subtrihedral in marginal outline, being rapidly narrowed posteriorly from the anterior portion; moderately gibbous, most so a little in front of its mid-length and above its mid-height; test somewhat thick; beaks placed near the anterior end, moderately depressed; umbones slightly raised above the hinge-line; umbonal ridge distinct, angular, and so prominent as to produce a flattened or even slightly concave space between it and the hinge-margin, giving the whole back of the shell a broadly flattened aspect; front margin regularly rounded from beneath the beaks to the basal margin, which latter margin is nearly straight or only slightly convex, especially behind the anterior third of its length; postero-basal margin narrowly rounded to the postero-dorsal margin, which meets the former

with an elongated downward and backward slope from the hinge-margin; the latter margin nearly straight, and occupying about two-thirds the whole length of the shell. Surface marked by only the ordinary lines and coarser imbrications of growth, but usually the angular umbonal ridge is cut across by three or four short, distinct ridges and corre sponding furrows, extending obliquely inward and backward, being scarcely perceptible in front of the umbonal ridge, and becoming obso lete before reaching the postero-dorsal margin, or at least only pro ducing slight sinuosities upon it.

Length 58 millimeters; height from base to umbones 34 millimeters; thickness 28 millimeters.

The elongate subtriangular outline, prominent and angular umbonal ridges, and broad, flattened dorsum of this species, are features that readily separate it from all other known forms, and, together with the seven other species associated with it (mentioned in the next description), show an extent and diversity of differentiation among these earlier species of Unionida that is hardly surpassed at the present day. Locality and position.-Upper part of the Laramie Group; Black Buttes Station, Union Pacific Railroad, Wyoming.

Unio aldrichi (sp. nov.).

Shell of medium size, transversely elongate, approximately oblong in marginal outline, a little higher posteriorly than anteriorly; moderately gibbous, especially along the umbonal ridge, where the shell is thickest; test moderately thick, becoming much so in old shells; beaks placed nearly one-third the length of the shell from the front margin, incurved, broad, but not very prominent, although the flattened umbo is raised above the level of the hinge-line; umbonal ridge prominent, subangu lar; postero-dorsal portion of the shell behind this ridge compressed, sometimes subalate; front portion of the shell moderately gibbous, and between this and the umbonal ridge the sides are distinctly flattened; anterior margin regularly, but somewhat narrowly, rounded down to the basal margin, which is nearly straight along the middle; postero-basal margin somewhat narrowly rounded, and extended upward and backward to the postero-dorsal margin; the latter margin sometimes truncated obliquely downward and backward, and sometimes so rounded as to give a more nearly square truncation to the posterior end of the shell; hinge-line long and straight. Surface marked only by the ordinary lines of growth, except all that portion which lies behind the umbona ridge. This portion is marked by numerous sharply raised, irregular lines or narrow ridges, with the intervening spaces wider than the ridges themselves, which, beginning almost imperceptibly just behind the umbonal ridge, extend backward with a greater or less upward curve to the dorsal and posterior borders. These raised ridges increase in number with the growth of the shell, in very small part by implantation, but mainly by bifurcation. They usually constitute a conspicuous

surface-feature of the shell, but in some examples they are more or less obsolete. Their character is similar to that of the markings upon U. senectus and U. primavus White, especially the latter.

Length of the largest discovered example 82 millimeters; height at mid-length 48 millimeters; thickness about 32 millimeters.

The specific name is given in honor of Mr. Charles Aldrich, formerly a member of the Survey.

Position and locality.-Upper part of the Laramie Group, Black Buttes Station, Union Pacific Railroad, Wyoming, where it is found associated with U. brachyopisthus, U. couesi, U. endlichi, U. propheticus, U. primæ rus, U. holmesianus, U. goniambonatus White, and apparently with one. or two other species of this genus.

Genus CORBICULA Mergele.

Corbicula cleburni (sp. nov.).

Shell large, subtrihedral in marginal outline; height from base to umbo equal to the extreme transverse length, moderately gibbous and its sides regularly convex, flattened or a little concave along the postero-dorsal portion, concave in front, where there is an almost defined lunule; test thick, or even somewhat massive in the case of old shells; dorsal line forming a somewhat regular convex curve from the beak to the posterobasal portion, which latter portion is abruptly, sometimes almost angularly, rounded to the base; basal margin almost regularly rounded up to the antero-cardinal margin, but its convexity is usually a little greatest in front of the mid-length; antero-cardinal margin straight or slightly concave, meeting the antero-basal margin at an obtuse angle or a promi nent abrupt curve; beaks prominent, elevated, curving inward and forward, and ending in a well-defined point when well preserved, as most of the examples are; lateral teeth strong, well developed, and finely crenulate; cardinal teeth well developed, the outer posterior one in one example showing faint crenulations, but otherwise of the ordinary character; pallial line distinct, somewhat distant from the margin; sinus small, directed strongly upward. Surface marked only by the usual lines and undulations of growth.

Height of the largest example 42 millimeters; extreme transverse length about the same; thickness 32 millimeters.

This species bears more resemblance to C. cytheriformis M. & H. than to any other published species; but it may be distinguished from that species by its more distinctly trihedral outline, its greater proportionate height, and its concave, almost lunulate front.

Position and locality.-Laramie Group, Crow Creek, Colorado, about 12 miles north of its confluence with South Platte River.

Corbicula cardiniaformis (sp. nov.).

Shell somewhat above medium size for a species of this genus, transversely subelliptical, moderately gibbous, especially a little forward of