TRENTON LIMESTONE. 173 
This species usually occurs as casts of the interior, the shell being rarely preserved. I 
have seen a single specimen in which some remains of the shell can be distinguished ; and 
there is also an obscure indication of the spiral band on the angular margin of the last 
volution, but the details cannot be made out. 
This species is probably the same as that described by Mr. SowErsy, cited above ; and 
its similar geological position is a further reason to regard it as identical. It possesses the 
essential characters of PLEuroromarta, which are better seen in the analogous succeeding 
species. 
This species is regarded by M. pe Verwneutt as identical with Euomphalus qualteriatus, 
cited above; but it appears to me that there are some reasons for separating it. That 
species, judging from the figures of ScutorHeim, WAHLENBERG, Hisincer, Goipruss and 
DE VERNEUIL, is less depressed than our shell, and the last volution below the angle more 
vertical and ventricose, giving the aperture a different form as represented by the authors 
quoted, that of WauLENBERG approaching more nearly to our shell, but being insufficiently 
extended transversely. In our specimens, the extent of the aperture, from the suture with 
the next volution, is greater than the vertical height ; while in the figures cited, except that 
of HistnceEr, the vertical diameter is equal to, or greater than, the transverse, and, in that 
of Gotpruss, nearly twice the transverse extent from the suture to the outer angle. Our 
specimens are very uniform in character, and we can scarcely conceive such a change to 
have taken place in the same species on the other side of the Atlantic. The succeeding 
species bears a more close resemblance to the E. qualteriatus, in the form of the aperture 
and expansion of the last volution. 
Fig. 6 a. View cf the spire (the specimen is a cast). 
Fig. 6 6. Lateral view, shewing the elevation of the spire. 
Fig. 6 c. Base of a smaller specimen (a cast), showing the umbilicus. 
Fig. 6d Front view of the same, showing the aperture. 
Position and locality. This fossil is more abundant in the higher crystalline portions of 
the rock at Watertown, than at any other locality. It is rarely found at Middleville, and 
other localities in the Mohawk valley. At the first named locality, it is more abundant than 
any other univalve in the rock, except the Bellerophon bilobatus. (State Collection.) 
224. 12. PLEUROTOMARIA ROTULOIDES (n. sp.). 
Pu. XXXVII. Figs. 7 a, b,c. 
Compare Euomphalus qualteriatus, and synonymy as in the preceding species. 
Depressed conical ; spire composed of about four volutions ; height about equal to half 
the width of the shell ; outer volution angular at the margin, ventricose below and slightly 
concave above ; upper ones becoming convex above, and slightly elevated vertically at the 
suture ; umbilicus small; aperture subquadrate ; surface marked by distinct sharp striz, 
which curve gently backwards from the suture above ; edge of the outer volution distinctly 
marked by a spiral band, with abruptly curving striz, indicating the marginal slit. 
