SEMELID^. 163 



Syn. — Amphidesma, Lamarck, 1818. 



Distr. — 60 sp. West Indies, Brazil, India, China, Australia, 

 Peru. Fossil, 30 sp. Eocene — ; United States, Europe S. 

 variegata^ Lara, (ex, 34). S. reticulata, Chemn. (ex, 35). 



Shell rounded, subequilateral, beaks turned forwards ; posterior 

 side slightly folded; hinge-teeth 2*2, laterals elongated, distinct 

 in the right valve ; external ligament short, cartilage internal, 

 long, oblique ; pallial sinus deep, rounded. 



Syndosmya, Recluz, 1843. 



Syn. — Abra, Leach, MSS. 



Distr. — Norway, Britain, Mediterranean, Black Sea, India. 

 Fossil, 6 sp. Eocene — ; Britain, France. S. aZ6a, Wood (ex, 36). 

 S. breais, I)esh. (ex, 37). 



Shell small, oval, white and shining ; posterior side shortest ; 

 umbones directed backwards ; cartilage-process oblique ; hinge- 

 teeth minute or obsolete, laterals distinct ; pallial sinus wide and 

 shallow. 



Animal with the mantle open, fringed ; siphons long, slender, 

 diverging, anal shortest, orifices plain ; foot large, tongue-shaped, 

 pointed ; palpi triangular, nearly as large as the gills ; branchiae 

 unequal, triangular. 



The species are few, and mostly boreal, ranging from the 

 laminarian zone to 180 fathoms. — Forbes. Thej^ live buried in 

 sand and mud, but when confined are able to creep up the sides 

 of the vessel with their foot. 



Theora, H. and A. Adams, 1854. 



Syn. — Endopleura, A. Ad. 



Distr. — 4 sp. Eastei'n seas. T. lata, Hinds (ex, 38). 



Shell compressed, transversely oval, smooth, polished, gaping 

 behind; ligament lodged in the cardinal pit ; pallial sinus pro- 

 found. 



A. Adams considers the species of Theora to be without 

 primary teeth, which certainly is not always the case. He conse- 

 quently suggests for a peculiar Chinese form with a " primary 

 tooth in front of the oblique cartilage-pit " and " with an internal 

 rib extending from the beaks obliquely towards the anterior 

 side," the name Endopleura as a subgenus. The internal rib 

 may be characteristic, but this is not the case as regards the 

 presence of cardinal teeth. 



The Theorge live in mud and sometimes brackish water. The 

 animal has a strongly compressed, linguiform foot, and two per- 

 fectly separated long siphons. 



Leptomya, a. Adams, 1864. 

 Distr. — 2 sp. L. cochlearis, Hinds. 

 Shell thin, ventricose, beaked posteriorlj'^ ; surface of valves 



