159 Couthouy's Monograph on 
simple or entire, instead of being, as in that species, 
double or divided in two portions. 
Its outline also approaches that of T. Ns 
Kiener, but it is readily distinguished by its roughness, 
and the very apparent stri& of growth which almost 
form plaits on the. extremities. T. phaseolina on the 
contrary, is quite smooth and the strie hardly percep- 
tible. 
It appears to vary aada hiii in its exta appear- 
ance, contour, &c., as in two specimens in my posses- 
sion, one is considerably longer than the other in pro- 
portion to its height, and more irregulaf in its outline. 
This variety has some likeness to the figure given by 
Dr. Turton of his Anat. truncata Brit. Biy. tab. 4, f. 6, 
the right valve having something of. a truncated aspect, 
anteriorly as well as posteriorly. 
Of the existence of the ossiculum spoken of by M. - 
Deshayes, there appears some trace in a slight impres- 
sion, visible on the under or inner surface of the liga- 
mentary apophyses, and it is possible one may-have been 
attached, and displaced through want of knowledge in 
the person who removed the animal. Still, this is very 
doubtful, as the specimens were otherwise very perfect, 
the thin membrane which lines the interior of the shell 
still remaining upon it, and in one the ligament was 
not in the slightest measure injured, great caution evi- 
dently having been used in taking out the animal. - 
