418 



MOLLUSCA 



SUB-KINGDOM VI 



Macoma, Leach. Anal siplion long, branchial very short, hinge without laterals ; 

 shell smooth, less elongated than in Tellina. Tertiary and Recent. 



Gastrana, Schum. (Fragilia, Desh.) Miocene and Recent. 



Quenstedtia, Mor. and Lye. Long, oval, obliquely truncate behind ; beaks low, 

 pallial sinus shallow, only a single cardinal tooth present. Jura. 



Abra upeli 

 near Vienna. 



FIG. 709. 

 Ben. sp. Miocene ; Grund, 



Family 34. Semelidae. DalL 



Resembling the Tellinidae, but with the resilium internal, often on a distinct chondro- 

 pJwre, and with the laterals, when 'present, stronger and less distant. Tertiary to Recent, 



Semele, Schum. (Amphidesma, Lam.) Shells large, rounded, thick, often conspicu- 

 ously sculptured ; 100 species. Tertiary and Recent. 



Cumingia, Sow. Small, thin, with a spoon- 

 like chondrophore ; habit nestling. Tertiary 

 and Recent. 



Scrobicularia, Schum. Differs from Semele 

 in having no lateral teeth. Tertiary and Recent. 

 Abra, Leach (Syndosmya, Recluz), (Fig. 769). 

 Smooth, small, thin ; cardinals 2 : 2, an anterior 

 and posterior lateral present ; chondrophore 

 narrow, oblique, not separated from the hinge line. Tertiary and Recent ; chiefly in 

 deep water. 



Family 35. Psammobiidae. Dall. 



Shell as in the Tellinidae, but usually more equivalve and less twisted, with more 

 conspicuous epidermis and nymphs, broader hinge 

 plate, and a wider posterior gape; lateral laminae 

 on the hinge wanting, and the cardinals sometimes 

 three in one valve; ligament external and conspicuous; 

 no defined area. Tertiary and Recent. 



Psammobia, Lam. (Gari, Schum.), (Fig. 770). 

 (?) Cretaceous. Tertiary and Recent. 



Pliorhytis, Conrad ; Asaphis, Modeer ; Sanguino- 

 laria, Lam. ; and Heterodonax, Morch. Tertiary and 

 Recent. 



Family 36. Donacidae. Deshayes. 



FIG. 770. 



(Cal " 



Valves equal, free, sub-trigonal, usually closed, 

 solid; outer surface and inner margins smooth or 

 radially sculptured, the posterior end usually shorter 

 and obliquely sub-truncate; pallial sinus similar in both valves ; resilium sub-internal, 

 sometimes amphidetic ; ligament short, external, seated in a deep groove, opisthodetic; 

 hinge plate moderately developed, usually with a posterior and anterior 'lateral in the 



right, and corresponding sockets in the opposite valve; cardinal formula STyTTviJ ^ ie 

 strongest cardinal tooth often bifid. Lias to Recent. 



The resilium is chiefly opisthodetic and sub-internal, but some of the large species have a 

 small segment of the /esilium separate from the rest, wholly internal, and in front of the 

 beaks. 



Isodonta, Buv. (Sowerbya, d'Orb.) Sub-symmetrical, convex, laterals strong, pallial 

 sinus deep. Jura. 



