LINQULID^. 341 



AcROTRETA, Kutorga, 1848. 



Distr. — 3 sp. Cambrian, Lower Silurian ; Russia, England, 

 Sweden. A. subconica^ Kutorga (cxl, 9, 10). 



Shell triangular ; large valve bullet-shaped, with a high area 

 and toothless hinge-margin ; end of the beak with round per- 

 foration ; surface not spiny. 



? YoLBORTHiA, Moller, 1814. 

 Distr. — F. recwrua, Kutorga. Silurian; Russia. 



Helmersenia, Pander, 1861. 



Distr. — Lower Silurian ; Russia. 



Shell nearly equivalve, rounded, small, horny-cretaceous ; 

 lower valve with slightl}'- produced beak, perforated, area narrow, 

 grooved ; upper valve with thickened hinge-margin ; muscular 

 impressions as in Obolus. 



Family LINGULIDJE. 



Shell oblong or orbicular, subequivalve, attached by a pedicel 

 passing out between the valves ; texture horny, minutely tubular. 



Animal with a highly vascular mantle, fringed with' horny 

 setae; oral arms thick, fleshj^, spiral, the spires directed inwards, 

 towards each other. 



Lingula, Bruguiere, 1789. 



Etym. — Lingula^ a little tongue. 



/SV^i.— Pharetra, Bolten, lt98\ Glossina, Phill, 1848. 



Distr. — 16 sp. India, Philippines, Moluccas, Australia, 

 Feejees, Sandwich Islands, West America, North Carolina. 

 Fossil, 140 sp. Lower Silurian — ; North America, Europe, 

 Thibet, L. anatina, Lam. (cxl, 11-13). L. Murphiana, King 

 (cxl, 141 



Shell oblong, compressed, horny, greenish, slightlj^ gaping at 

 each end, truncated in front, rather pointed at the umbones ; 

 dorsal valve rather shorter, with a thickened hinge-margin, and 

 a raised central ridge inside. 



Animal with the mantle-lobes firmly adhering to the shell, and 

 united to the epidermis, their margins distinct, and fringed all 

 round ; branchial veins giving off numerous free, elongated, narrow 

 loops from their inner surfaces ; visceral cavity occupying the 

 posterior half of the shell, and surrounded by a strong, muscular 

 sheath; pedicel elongated, thick; stomach long and straight, 

 sustained by inflections of the visceral sheath ; intestine convo- 

 luted dorsaily, terminating between the mantle-lobes on the right 

 side, oral arms disposed in about six close whorls, their cavities 

 opening into the prolongation of the visceral sheath in front of 

 the adductors. 



