LINGULIDA. 341 
Acrotreta, Kutorga, 1848. \ 
Distr.—3 sp. Cambrian, Lower Silurian; Russia, England, 
Sweden. A. subconica, Kutorga (exl, 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. 
?- VorBorTHtaA, Moller, 1874. 
Distr.—V. recurva, Kutorga. Silurian; Russia. 
HELMERSENIA, Pander, 1861. 
Distr.—Lower Silurian; Russia. 
Shell nearly equivalve, rounded, small, horny-cretaceous ; 
lower valve with slightly produced beak, perforated, area narrow, 
grooved; upper valve with thickened hinge-margin; muscular 
impressions as in Obolus. 
Famity LINGULID 2. 
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 
sete ; oral arms thick, fleshy, spiral, the spires directed inwards, 
towards each other. 
Lineuta, Bruguiere, 1789. 
Ktym.—Lingula, a little tongue. 
Syn.—Pharetra, Bolten, 1798. 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. JZ. anatina, Lam. (exl, 11-13). L. Murphiana, King 
(exile 14): 
Shell oblong, compressed, horny, greenish, slightly 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 dorsally, 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. 
