32 
NOMENCLATURE. 
dor sat a. Dorsal ; the back obtusely keeled. 
edentula. Toothless, with reference to the mar- 
gin. 
hiafis. Gaping; the valves so partially closing, 
that the margins do not every where touch 
each other. 
injiexa. Inflex ; bent towards the anterior slope. 
Imguiformis. Linguiform ; tongue-shaped, linear 
with the extremities obtusely rounded. 
navicularis. Navicular ; boat-shaped. 
l^ectinata. Pectinate ; longitudinally sulcate or 
striate ; the striae forming an acute angle 
in the anterior part. 
radiata. Radiate ; with diverging rays flowing 
from the apex longitudinally to the cir- 
cumference. 
rostrata. Rostrated ; the anterior extremity elon- 
gated and narrowed. 
fastigiata. Fastigiate ; terminating transversely 
at the base. 
saccata. Saccate; distended towards the beaks. 
truncata. Truncate ; part of the circumference 
being abrupt, or, as it were, cut off. 
