If we except the beak, the outline of this shell, as respects the hinge margin and the sides, considerably resembles that of P. spinulosus of Sowerby, but the base is far more obtusely rounded, and it is a shorter shell comparatively with its width. The serratures are very often broken off. The curvature of the sides does not in the slightest degree project beyond the angles of the hinge line.
13. An imperfect cast, very like the terebratula subundata of Sowerby, and of equal magnitude.
14. Pentagonal ossiculæ of the trunk of encrinus of authors, which in outline may be compared to figs. 61 and 62, of plate 13. vol. 2. of Parkinson's Organic Remains, but their surfaces do not now exhibit any sculpture.
15. Many of these shells exhibit the most unequivocal evidences of having been in a plastic state, at some period or other, since their deposition in their present situations. The fine striæ of a productus lineolatus, are so interlaced on the middle of a valve of one of our specimens, as at once to convince every observer of the shell having been thus partially dissolved, and when in this state to have been gently rubbed by some other body, in two directions proceeding obliquely to the same point, so as to throw the striæ in that part entirely out of their proper longitudinal direction. It is very common to find shells unnaturally flattened, or compressed in various ways and degrees, often without any fracture in the shell or cast; a circumstance which certainly could never happen to the shell, unless it was in a plastic state, or in a state of partial solution.
16. A specimen of carbonate of lime, on its surface a mass of sub-parallel tubes, connected by short lateral processes. The whole much resembles, and is probably congeneric with the erismatholithus tubiporites (catenatus) of Martin's Petrif. Derbi. t. 42. fig. 2., but the connecting processes of the tubes are much shorter than they are represented in that figure; but it corresponds much more exactly with the tubiporite, figured by Parkinson in his Organic Remains, vol. 2. pl. 1. f. 1., and may with great propriety form a new genus, the type of which will be the tubipora strues of Lin.
The genus is probably allied to favosites and tubipora.
17. Trilobus.—The abdomen of a species of this singular genus frequently occurs in the sandstone of the Missouri; near Engineer Cantonment they were very common. The largest was rather more than one inch long, by about one and three-tenths inches in breadth at base; but the more general length is about three-fourths of an inch. The tergum or intermediate lobe is narrow, being not more than two-thirds of the width of the flanks, and much more convex than those parts.
But a single specimen occurred, which we can, without any doubt, consider as the thorax of a trilobus; but whether or not it appertains to the same species with the above, or to some other of which we have no other fragment, we are at a loss to determine. Like the above-mentioned abdomen, it is distinct from any that we have seen figures of. It is of a narrow lunate form, highly convex, the disk destitute of sculpture, and the eyes prominent.
18. Many imperfect casts of two different kinds of bivalve shells occur near Engineer Cantonment, of which one may possibly have been a cardita.
19. Tooth of a squalus, which seems to approach nearest to those of Sq. maximus, by its compressed conic form.