Remarks
shark-references Species-ID=5384;
Original diagnose after Whiteaves (1889) p. 191-192 [2542]: Tooth (in the only specimen known to the writer) very small for the genus: the crown conical, with obliquely compressed sides, its maximum height being about equal to its breadth at the base, though, as its apex is somewhat worn down from use, its original height may have slightly exceeded its breadth. Outline of the base of the crown, as viewed from above, somewhat quadrangular and much longer than broad, but its posterior end is deeply excavated in the centre and produced on both sides into a small and short process, which expands slightly outward and is truncated and minutely grooved at its termination. Lateral outline of the base of the crown, shallowly concave: characters of the root unknown. At the anterior end of the ci-own there is a triangular smooth space, but the rest of its surface is marked by corrugations or ridges, which appear to have crossed the summit and posterior end continuously. At the posterior end the continuity of three of the corrugations or ridges. from the base of one side to that of the other, is still clearly visible, and there is a certain amount of regularity in their disposition. In the central portion the wearing down of the summit has destroyed their continuity, and on the sides the corrugations are so much abraded as to be nearly obsolete. Near the anterior end the corrugations on the sides are more irregular in their shape and disposition than at any other part of the surface, and those which correspond to each other, on the two opposite sides, are seldom, if ever, exactly alike. Thus, on the right hand side of the crown, one of the corrugations close to the front branches three or four times below the middle, and its longest branch bends inward at nearly a right angle to the main stem and to the rest of the corrugations, but this is not the case with the corresponding one on the opposite side, and in no part of the surface do the corrugations cross each other sufficiently often to form a complete, or even partially complete, network. Under a lens also, the external orifices of the dentinal tubuli are plainly visible through the polished transparent enamel, and where the latter is worn away, as on the summit and at the anterior end, the orifices themselves are exposed and appear as closeset punctures of irregular shape. Dimensions of the only specimen collected: maximum length of the crown, nine millimeters and three-quarters; actual height of the crown, as measured in the centre, six mm; breadth of the crown at ils base, also as measured in the centre, six mm. Swan River, below Thunder Hill, J. W. Spencer, 1874: one specimen, which consists of the whole of the crown and a small portion of the roots of one of the palatal teeth. From the Niobrara group, or upper part of the series. In its general shape, especially as seen from above, and in the peculiar ornamentation of its crown, this tooth appears to differ from those of any of the previously characterized species of Ptychodus from the Cretaceous rocks of North America, but, until a larger series of specimens shall have been obtained, its specific relations must remain doubtful.

valid after Whiteaves (1889) p. 191-192 [2542];

synonym of Ptychodus whipplei (?, badly worn) after Bardack (1968) p. 146 [11504];

References