200 CONTRIBUTIONS 
the anterior part, are combined, two or three together, 
leaving a furrow between each association. On the pos- 
terior part, these striz are single, but disordered by the 
transverse folds, which exist only on that part of the valve. 
NM. semen. Plate 6. Fig. 214. 
Description. Shell transversely elliptical, rather inflated, 
furnished with large concentric folds and with a deep fur- 
row on the anterior slope, rostrate behind; substance of 
the shell rather thin ; lunule and escutcheon both lanceo- 
late ; beaks small, rather pointed; margin entire; nacre 
not pearly. 
Diam. 1-20th, Length -1, Breadth 3-20ths, of an inch. 
The smaller figure is of the size of nature. 
Observations. A single specimen only of this species 
has come under my notice. It consists of the two valves 
attached. I endeavoured to separate the valves to ex- 
amine the teeth, but with the greatest precaution was 
unable to effect it, one of the valves becoming fractured ; 
therefore, the teeth are not mentioned in the description. 
This is a very minute species, remarkable for its large 
concentric folds and the deep furrow on the posterior slope. 
It has some resemblance to the mucronata of Sowerby, 
Min. Conch., pl. 476. 
Bulla Dekayi.* Plate 6. Fig. 215. 
Description. Shell subfusiform, transversely striate 
* Named after my friend Dr Dekay of New York. 
