« EelmineJätka »
The specimens that have come under my observation have in general the same amount of convexity, the depth of both valves being in all about two-thirds the greatest width.
The surface is nearly smooth; a few obscure concentric undulations of growth and fine striæ,-of the latter, twelve to fifteen in the width of one line are visible on well preserved shells. There are also faint indications of longitudinal radiating lines. A fragment of one individual of this species exhibits a surface uniformly marked with fine rounded concentric undulations (not striæ), of which there are four of five in the width of one line.
This species has, to some extent, the aspect of a Pentamerus ; but its internal structure, as exhibited in the numerous broken specimens that I have examined, shews it to be congeneric with A. Clara. It differs from that species in having the mesial fold and sinus extending the whole length of the shell, and the beak of the ventral valve not touching the umbo of the dorsal valve.
Locality and formation. --St. Mary's, Township of Blanshard. Corniferous.
Collectors.-Mr. W. G. Tomkins, C. E., St. Mary's, C. W.; A. Murray; J. Richardson.
ATHYRIS (?) Scitula.—(Hall.) ATRYPA SCITULA.—Hall. Geology of the Fourth District of the
State of New York, p. 171, fig. 1.
The above figures represent different views of two specimens of a species which appears to me to be identical with that figured in the work above cited. It varies greatly in size. The length of the
largest specimen that I have seen is seventeen lines, the greatest width fourteen lines, depth eight lines. The smallest is about two lines in length, and many of intermediate sizes have been observed to make out the series. It is not certain that this species belongs to the genus Athyris.
Locality and formation.- County of Haldimand. Corniferous Limestone.
Collectors.-J. De Cew, E. De Cew.
ATHYRIS (?) Clusia.-N. Sp. Description.-Elongate oval; greatest width at about one-fourth the length from the front margin ; sides diverging at an angle of about 75o and somewhat straight, or gently convex, for rather more than half the length; front angles rounded; front margin nearly straight, or gently convex. Both valves depressed convex, smooth in the upper half, the front margin with four or five wide shallow concave indistinct folds or grooves which become obsolete at less than half the length. Beak of ventral valve erect, apparently a little incurved at the tip.
Length five lines ; greatest width at one-fourth the length from the front margin, three lines; depth of both valves at one-third the length from the beak, one line and one-fourth.
The above description is founded on a single small specimen. I have seen a fragment of another that must have been, when perfect, seven lines in length, and I am inclined to think that the one described is a young individual of the species.
This species differs from A. scitula, principally in being proportionally much flatter, and in having the front margin undulated by several obscure folds.
Locality and formation.—Lot No. 45, Con. 1, Cayuga. Corniferous.
Collector.-J. De Cew.
ATHYRIS (?) UNISULCATA.—(Conrad.) ATRYPA UNISULCATA.-Conrad. Annual Report Geological Survey,
New York. 1841, p. 56. RHYNCONELLA UNISULCATA.-Hall. Tenth Annual Report of the
Regents of the University of the State of New York. 1857, p. 125.
Fig. 39, Athyris unisulcata -Ventral view,
Description ---Shell quadrilateral or sub-triangular ; greatest width near the front margin ; sides nearly straight from the beak to the line of the greatest width, where there is a prominent angle on each side of the shell, thence converging and nearly straight to the middle of the front margin. Dorsal valve with a mesial fold which occupies the whole of the shell except a small portion on each side in the upper half; the slope from the ridge of the fold to the sides usually gently
In some specimens a single strongly impressed groove along the ridge of the mesial fold. The ventral valve has a deep mesial sinus equal to its whole width; a small strip of the margin between the beaks and the point of the greatest width inflected at a right angle or thereabout towards the dorsal valve. The beak is incurred over the umbo of the dorsal valve, but its tip not quite in contact with the surface of the dorsal shell. The surface is nearly smooth, a few obscure concentric undulations, and, in some specimens, indications of fine radiating striæ visible.
Length of large specimen, nine lines ; width, eleven lines.
This species varies greatly in form. Some have the front margin nearly straight, and are thus almost triangular. Others are quadrangular or rhomboidal from the great projection in the middle of the front margin. The sinus of the dorsal valve is sometimes so shallow
* These figures are not very good, but as they will serve to give an approximate idea of the form of one of the varieties, I have thought it best to use them.
that the valve has the appearance of a flat space along the middle. The groove on the ridge of the dorsal valve either extends to the front margin of the shell, or dies out at a greater or less distance from the beak.
The length of the shell ranges from two to nine lines, and is always a little less than the width.
Locality and formation.-County of Haldimand. Corniferous Limestone. Not common.
Collectors.-J. De Cew, E. De Cew, and E. Billings.
ATHYRIS (?) ROSTRATA.-(Hall.) ATRYPA ROSTRATA.-Hall. Geology of the Fourth District of New
York, page 202, fig. 2.
Description.-Elongate oval, both valves evenly convex and smooth. Ventral valve the larger, most ventricose in the upper half; beak proportionally large, sub-cylindrical, incurved, not in contact with the umbo of dorsal valve, apparently perforated by a large foramen. Dorsal valve smaller than the ventral, but proportionally as strongly convex, umbo rather broadly rounded, beak incurved and deeply buried beneath that of the ventral valve.
Length about six lines; greatest width a little in front of the middle of the ventral valve, five lines ; depth of both valves a little above the middle, three lines and a half.
The surface at first sight appears to be quite smooth, but upon a closer examination it will be found to exhibit some fine obscure concentric rings of growth.
This neat little fossil is smaller and proportionally broader, and more ventricose than A. scitula.
Locality and formation.-Lot 26, con, 3, Bosanquet. Hamilton Shales.
Collectors.-A. Murray and J. Richardson.
Description.-Transversely sub-oval; greatest width usually about the middle, sometimes a little above or below; front margin often with a rounded projecting lobe in the middle ; both valves convex. Ventral valve with a concave mesial sinus which occasions a linguiform projection in the middle of the front margin, and becomes obsolete at about half the length of the shell; umbo well defined ; beak closely incurved down to the umbo of the dorsal valve, usually, if not always, perforated at the tip by a small circular aperture. Dorsal valve with a rounded mesial fold which elevates the middle of the front margin and becomes obsolete at about half the length.
Surface with somewhat obscure rounded but apparently much depressed, simple or undivided radiating ribs, of which there are on an average in the specimens examined, three in the width of one line. There are also, especially towards the front margin, a few squamose rings of growth. There appear to be some fine concentric striæ, but the surface in the specimens is not quite perfect.
Width, from five to nine lines; length, a little variable, according to the greater or less developement of the mesial fold.
In one specimen with the fold large, the length is seven lines to a width of nine lines.
In this species I have detected no appearance of an area, but in perfect specimens the hinge-line is extended to three-fourths the width of the shell, and in such cases the cardinal angles, although rounded, are elevated and much compressed.
Locality and formation.-Lot No. 26, con. 3, Bosanquet. Hamilton Shales.
Collectors.-A. Murray, J. Richardson.
(To be continued.)