418 MOLLUSCA SUB-KINGDOM VI 
Macoma, Leach. Anal siphon long, branchial very short, hinge without laterals ; 
shell smooth, less elongated than in Tellina. Tertiary and Recent. 
Gastrana, Schum. (Fragilia, Desh.) Miocene and Recent. 
(uenstedtia, Mor. and Lye. Long, oval, obliquely truncate behind; beaks low, 
pallial sinus shallow, only a single cardinal tooth present. Jura. 
Family 34. Semelidae. Dall. 
Resembliny the Tellinidae, but with the resilium internal, often on a distinet chondro- 
phore, 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. 
Serobicularia, Schum. Differs from Semele 
in having no lateral teeth. Tertiary and Recent. 
Abra, Leach (Syndosmya, Récluz), (Fig. 769). 
ft ae Ren. sp. Miocene; Grund, 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. 

Fic. 769. 
Family 35. Psammobiidae. Dall. 
Shell as tn the Tellinidae, but usually more equivalve and less twisted, with more 
conspicuous epidermis and nymphs, broader hinge 
plate, and a wider posterior gape; lateral laminac 
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 Heterodonaz, Morch. Tertiary and 
Recent. 
Family 36. Donacidae. Deshayes. 

Valves equal, free, sub-trigonal, usually closed, Fic. 770. 
solid ; outer surface and inner margins smooth or gion ena ee Desh. Hocsns’ (Cals 
radially sculptured, the posterior end usually shorter ae 
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 aoe the 
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 resilium separate from the rest, wholly internal, and in front of the 
beaks. ; 
Isodonta, Buy. (Sowerbya, d’Orb.) Sub-symmetrical, convex, laterals strong, pallial 
sinus deep. Jura. 
