clustered on Actinocrinus-which is rare-neither worn nor eroded, and otherwise specially marked. One has first accommodated a Crania, subsequently the clustered coralloid under consideration; another was first the resting-place of a Crania, then of the coralloid, and afterward of the basement portion or foot of a young crinoid (specimen D). What a throng of life! More remarkable still, the third is an example of a cluster of great rarity, and appears to have been constructed on a living crinoid! This specimen is most instructive; the stem had evidently continued to grow, while the spot occupied by the coral patch seems to have been arrested in growth (specimen E). This specimen, glanced at and put aside for examination during the past sixty years, is the only example noted as bearing evidence that the polypi engaged in the process of construction adopted a living encrinite as the field on which to labour. Two other specimens are notable, because On short stems of Poteriocrinus, the cluster on each covers the entire joint-disc or end of ossiculi, passes over the edge on to the stem, encircling what may be supposed to have been the only exposed part, the other end having been fixed in the mud (specimen F). Hence it is certain that Stenopora tumida did encircle stems when placed favourably for the operation. How this coralloid clung so closely to old worn stems of Poteriocrinus crassus as a building station may be a question difficult to solve.

rare.

2. Archaeopora nexilis.—Of this polyzoon thirty specimens were likewise examined, all-with rare exceptions-attached to small and short well-preserved or unworn crinoid stems. Fifteen of that number encircle, but do not in any instance pass on or over, the ends of the stems (specimens A, B, C). Twelve are on Poteriocrinus, two on Rhodocrinus, and one on Actinocrinus. Fifteen others do not entirely complete the encircling process, nor do they pass over or on the ends of the stems; of which number eleven are on Poteriocrinus, three on Actinocrinus, and one on Rhodocrinus. The fabric of this species is thin, comparatively equal or smooth, not exceeding in thickness a calling card on an average, and in every instance that structure, when the crinoid on which it is constructed has been broken, or at severed joints, is found irregularly fractured. Encircling of the stems, and their freshness, implies that the crinoids had been erect during the operations of the special polypi; and it may be farther implied that the crinoids lived while the construction proceeded.

3. Diastopora megastoma.-Thirty specimens were examined. The fabricators of this structure follow those of Archaeopora in their style and manner of work, although less deftly finished, and likewise in selecting small stems, not worn or tarnished, on which to squat. They seem, too, to have constructed their characteristic fabric when the crinoid was in the erect position,-including in the web short broken branches, which are seen or indicated by irregularity of surface,—and also of encircling the crinoids without passing on or over the ends of the stems-hence, probably, when alive. The substance or mass of the organism is from two to six times thicker than the more delicate and ornate Archaeopora. Of the thirty specimens examined it has been found that twenty encircle the stems, thus: eleven on Rhodocrinus, seven on Poteriocrinus, and two on Actinocrinus. Nine, which do not encircle completely, consist of seven of Poteriocrinus, and two of a species of Rhodocrinus.

It would thus appear that Stenopora tumida had been constructed in clusters, almost exclusively on large and dead stems, and their form and limits suggest the idea that these stems must have been partially sunk in the mud. It is equally apparent that Archaeopora had been constructed on small, erect, perhaps living stems and branches, conditions which equally apply to Diastopora.

Now the primary object of this examination was a search for evidence of a repelling agency, or of a defensive or protective force exercised by crinoids infested by irritating parasites. One would naturally conclude in the case of the two last-mentioned species, that if any resistance had been made in any form to the progressive course of the aggressive action, it would have been found in connection with these encircling polyzoa. Nothing of the kind has been observed. But, where least expected, it has been found that a fragment of Actinocrinus has attached to it a fine specimen of Stenopora tumida, which, after construction, seems to have repressed or hindered the growth of the crinoid, so far as the cluster extended, while beyond the edges of that cluster the stem is enlarged, giving the specimen the appearance of being slightly sunk in the stem, or what amounts to the same thing, the stem is raised or bulged above the level of the invading body, and presents throughout a corresponding general enlarged and healthy condition. Such an operation is undoubtedly the result of lifeaction; but there is no evidence that this action was, in the

smallest degree, either protective or defensive in design or character.

That the fragments of crinoids were more suitable than other marine exuviae for parasitic constructions is unlikely; but they may, probably, have been more abundant in the oceans of the Carboniferous eras. These structures are apt to puzzle young palaeontologists, for long observation is often necessary to interpret what is oftenest seen. Nothing is more common, for example, than the basement portion of crinoids, but it may be long before connection of parts establish their nature.

The same thing may take place with regard to the basement or root portions of the polyzoa, often found on crinoids without stem or frond. A few specimens of this order may be described to exemplify the fact:

1. A fragment of encrinite, fully half an inch long and 2 lines diameter, has evidently an adventitious structure on one side, of calcareous matter, and irregularly rounded in form; thin, but with strong strengthening bands, on which appear fine striations and several raised small round apertures. The construction, in this instance, may be mistaken for the work of Serpula.

2. Another fragment, similar in most respects, but less perfectly marked.

3. A fragment of encrinite, with the tumid or diseased aspect, has on one end a very distinct structure, identical in character with the two previous specimens; but, in addition, the frond of a Fenestella is in connection, bearing strong evidence of having been based and supported on and by the structure. Thus a puzzle of long duration was solved. This specimen has the characteristic perforation on one side, with other characteristics common in injured crinoids; but somewhat strangely, the hole in the side is occupied with the root and part of the stem of another polyzoon. This is a most interesting and instructive specimen.

4. Is a small bit of encrinite, with a comparatively large tubercle of adventitious calcareous substance, which seems set in, rather than on, the fragment, it being contorted somewhat, and interrupted in development. This is seen distinctly in the lower ossicle, as well as in the depression of the stem. This structure must have been made during the life of the animal. The tubercle, although without characteristic striations, seems, in structure, to be the same as those described as roots of polyzoa. The genius

of life, put in play to form a basement for a polyzoon, had to depart from the well-established mode, in order to produce a projection beyond the surface line of a living encrinite. A little light is shed on the phenomenon by observing that on the upper side of the tubercle, and there only, a part of the stem exists, as seen in the other examples.

Petalodus Hastingsiae, Owen.

In forming a polished cross-section of the tooth of Petalodus Hastingsiae, characters were observed of much interest, tending to give edge and strength,-much in the manner of the blacksmith inserting a piece of steel between plies of iron in the axe to admit of a fine edge, which the iron incasement tends to prevent from petty fractures or destruction. This tooth, in section, is conical, half as broad at the base of the crown as the entire length. The whole crown is covered with enamel not thicker than the edge of a sheet of note paper, and apparently this delicate covering meets so as to form the cutting edge. But a mid-bar, apparently of enamel, forms the true cutting edge, which passes centrically between them for nearly half the length of the crown. About one-third of the length of the tooth from the cutting edge is white (bone-like, with the mid-bar distinct), the rest dark within the enamel. The white part has, on each side of the mid-bar, delicate lines passing between it and the outer enamel. The cutting edge is produced, technically, by a short cannel or abrupt finish.

These remarks probably comprehend all the particulars of structure as seen in section, and inferences. But a few words more may be said in reference to M'Coy's description of this tooth (Brit. Pal. Fossils, page 635). He states that "the cutting edge alone being marked with a row of punctures (twelve in one line); when worn, however, a fine line extends from each of these punctures half way down the crown, producing a structure scarcely visible to the naked eye." Now this description, true to the facts observed by him, admits of explanation. Between the external enamel and the mid-bar described above, which forms the cutting edge, numerous partitions of bone, with equally numerous interspaces, are easily discerned on each side of the cutting edge, and these extend as far down the tooth as the mid-bar reaches. An interpreter is needed at this point. This fish sharpened its own teeth, and it was easier and more fit to grind a partitioned

structure than more solid bone. The "twelve punctures in one line" of M'Coy are not distinctive. Strictly, there are two lines of puncture-like spaces, one on each side of the cutting edge, amounting in specimens under examination to 12 per inch, or 144 in each, in a tooth measuring fully an inch broad at the widest part of the crown, or laterally, and three-fourths of an inch long.

III.-Notes on the effects of Smoke on Vegetation, with a list of Trees and Shrubs specially adapted for planting in the neighbourhood of large towns. By Mr DUNCAN M'LELLAN, Superintendent of Public Parks.

It is almost unnecessary to say that smoke is injurious to vegetation. In the neighbourhood of large towns and of chemical works, for instance, where great quantities of smoke are daily emitted, vegetation as a rule does not nearly come up to the usual standard of nature. The moisture which is so prevalent in our northern climate does not help to alleviate this evil, but only renders it worse, soot being much more liable to adhere to a wet surface than to a dry one. Evergreens are more susceptible to injury from this cause than deciduous trees and shrubs, which is to be accounted for by the fact that their pores are constantly exposed over the whole year to the sulphureous gases and smoke. Deciduous trees, on the other hand, have the advantage of throwing off their faded summer foliage, and of enjoying a rest of several months, so that during that period, the worst of the year for vegetation, they escape most of the injurious effects of smoke, little or no sap circulating through the bark. In spring, as we see at present, nature renews their suits of foliage, to be cast aside when they have served their purpose.

The varieties of deciduous trees and shrubs which are late of bursting into leaf are those best suited for planting in towns. The earlier sorts are liable to injury from the cutting east winds which are prevalent in spring, and the foliage then being tender cannot withstand the bad effects of smoke. The constitution of the plants is thus impaired year by year, and they very soon sicken off and die. Amongst evergreens the Coniferae or fir tribe are the first to suffer from smoke, owing to the resinous nature of their bark and spines, which retain almost every particle of soot that falls upon them. Portugal laurels, Laurestinas, and