TRENTON LIMESTONE. 
177 
228. 16. PLEUROTOMARIA PERCARINATA (». sp.). 
Pl. XXXVIII. Fig. 4. 
Somewhat obtusely conical, ventricose ; spire short, obtuse ; volutions three or four, 
rounded, marked by numerous spiral carinae, which are crossed by vertical or undulating 
striae ; aperture not distinctly visible, but apparently it is broadly oval or rounded ; 
umbilicus none. 
This species is readily distinguished from all the others known in this rock, by the 
numerous spiral elevated ridges or carinae which mark the surface. It approaches very 
nearly in character to the Pleurotomaria bilix of Conrad ( Jour. Acad. Nat. Sciences , Vol. 
viii. pag. 211, pi. 16, fig. 10); but differs from that shell in being more ventricose, and 
in the volutions being rounded above, while in that species they are flattened, and abruptly 
contracted below, giving it a more trochiform aspect. 
This species and the preceding one differ from Pleurotomaria in the form of the 
aperture, and approach in this respect to Murchisonia. 14 
Position and locality. In the compact blue limestone, upper part of the Trenton limestone, 
Middleville. 
229. 6. MURCHISONIA BICINCTA. 
Pl. XXXVIII. Figs. 5 a - h. 
Compare Pleurotomaria angulata, Sowerby in Sil. Researches, pag. 641, pl. 21, fig. 20. 
Obliquely subconical ; spire elevated, acute ; volutions four or five, angular, rapidly 
enlarging towards the aperture ; last one ventricose below, tricarinate, the lower carina 
hidden by the suture of the next volution at the upper inner angle of the aperture ; central 
carina on the outer angle of the volution, margined on either side by a sharp elevated 
line, with a narrow groove between, producing a double spiral band ; aperture oblong, 
angulated below ; surface marked by fine sharp striae, which bend gently backwards, and 
are but slightly undulated in passing the first carina, from whence they turn more suddenly 
backwards to the mesial band, making an abrupt retral angle, and then bending forwards 
below, pass in a vertical direction to the suture. In the last volution, the striae pass vertically 
to the lower slight carina which corresponds with the suture in the other volutions, and 
from thence bend slightly backwards, curving into the umbilicus. 
The minute description here given will be found perfectly applicable to entire and un¬ 
worn specimens ; but it is often found in fragments and casts, with the surface markings 
more or less obliterated. The double spiral band becomes obsolete, and only a single ridge 
is manifest; the lower carina on the last volution is not visible in casts, and there is but 
an obscure indication of the upper one. The entire casts, therefore, present scarcely more 
than the single marginal angle, indicating the direction of the mesial band, and, in this 
respect, correspond with P. angulata cited above ; but the volutions in our shell are more 
ventricose. 
| Paleontology.) 
23 
