198 CONTRIBUTIONS 
much, from any species, fossil or recent, which has come 
under my notice. It possesses transverse folds on the sides, 
which lie closely to, and are beautifully parallel to each 
other. These terminate in a smooth plane, on the umbonial 
slope, which is flattened. A straight furrow, or channel, 
passes along the posterior dorsal margin, in which are strize, 
slightly oblique. The posterior series of teeth, as far as it 
exists in this fragment, is straight, and possesses nineteen 
angular teeth. From the appearance of this part of the 
series, I should not be surprised if it possessed almost as 
many more. The substance of the shell is thick, and it is 
suspected, that when found perfect, it will prove to be the 
largest species yet described. This fragment certainly 
warrants such a conclusion. 
NM. carinifera. Plate 6. Fig. 212. 
Description. Shell triangular, inflated, deeply truncate 
behind, minutely and concentrically striate, furnished with 
an elevated sharp carina on the umbonial slope ; substance 
of the shell thick; lunule cordate ; beak high, incurved 
and recurved ; posterior slope irregularly flattened, nearly 
circular, and furnished with indistinct longitudinal and 
transverse striz ; anterior series of teeth short, consisting of 
five teeth, and forming a sharp angle with the posterior 
series ; teeth rather large, angular ; fosset placed above the 
teeth, at the point of the beak ; nacre not pearly. 
Diam «er Length.... Breadth.... 
The lower figure represents the posterior slope. 
Observations. It is to be regretted that the description 
