MARYLAND GEOLOGICAL SURVEY 639 



Family CUSPIDAR1DAE 



Genus CUSPIDARIA Nardo 

 [Ann. Sci., Lombardo Veneto, vol. x, 1840, p. 49] 



Ty/ic. Tellina cuspidata Olivi. 



Shell minutely pyriform in outline, feebly inequivalve, strongly inequi- 

 lateral, the anterior portion of the shell inflated, the posterior abruptly 

 constricted and compressed; squarely truncate, gaping. 



" The shells of Cuspidaria possess an internal ligament, received in 

 each valve in a more or less differentiated groove or fossette, which may 

 project from the umbonal angle of the hinge margin, or be more or less 

 adherent to the anterior or posterior slope of this angle. They may have 

 one anterior and one posterior cardinal and lateral tooth in valve, any 

 one of which (or all in the genus ? Myonera) may be entirely absent. 

 Beside the teeth the hinge is reinforced in many cases by a buttress 

 extending in a direction vertical to the valve from the hidden surface of 

 the hinge margin, posterior to the umbonal angle. This buttress may 

 consist of the vertical plate above mentioned and a thickened rib curving 

 round in front of the posterior muscular scar, and then directed poste- 

 riorly, becoming almost immediately obsolete. Or the posterior muscular 

 insertion may be elongate and narrow, and the buttress take the form of a 

 " clavicle " or myophore, elongated, parallel with the posterior hinge 

 margin and separating the two posterior muscular scars. The muscles are 

 not always inserted upon the buttress, but may be above and in front of 

 it. Its purpose would seem to be that of strengthening the valve, almost 

 always thin and fragile, against sudden contractions of the muscles, and 

 to support the cardinal border, and especially the strong posterior lateral 

 tooth found in many species. When this tooth is found in a species which 

 has no posterior lateral in the other valve, the valve which has a tooth shows 

 the buttress stronger than the other, indicating its function as a support 

 for the tooth ; but when elongated and clavicular there is little difference 

 between the buttresses of opposite valves, indicating that in such cases 

 the function is the strengthening of the valve itself. The presence of 

 the buttress is. in my opinion, important only in a minor degree, except 



Etymology: Cuspis, cuspidis; a lance, a point. 



