BIVALVIA. 23 
Or 
elongated, lateral tooth on the anterior side, and one lateral tooth on the posterior 
slope, beyond the large and prominent fulcrum for the ligament; this fulcrum is so 
conspicuous, as almost to justify the species being placed in the genus Psammobia, and 
forms one of the links that so closely unite that genus with Ze//ina. The left valve has 
one large triangular cardinal tooth, and a rudimentary one behind it, with correspond- 
ing elevations or teeth, which fit into the lateral depressions of the right valve; and 
there is an obscure diagonal ridge on the inside, from beneath the umbo towards the 
anterior side of the ventral margin. The palleal scar is not well defined in our shell, 
but is probably very large and deep. 
Tellina tenuis is enumerated in Mr. Smith’s ‘ List of the Clyde Fossils.’ 
TRIGONELLA. Da Costa. 1778. 
SpoonmMussEL. Petiver. Lavienon. Cuv. 1817. 
Macrra (sp.) Gmelin. Lurrarta (sp.) Lam. 1818. Swains. 1840. 
Mya (sp.) Chemn. Listera. Turt. 1822. 
TELLINA (sp.) Donov. Lurricona. Blainv. 1824. 
LreuLa (sp.) Mont. 1808. AMPHIDESMA (sp.) Flem. 1828. 
SoLEN (sp.) Olivi. CALCINELLA. Agass. 1842. 
ARENARIA. Megerle. 1811. SEMELE (sp.) Woodw. 1854. 
ScropicuLaria. Schumacher. 1817. 
Generic Character. Shell equivalved, subequilateral, somewhat compressed, nearly 
smooth. Hinge furnished with two small cardinal teeth in the right valve, and one 
in the left; no lateral teeth. Muscular impression ovate. Palleal sinus large and 
deep. Ligament small, external. Cartilage large, internal. 
Animal with its mantle open, having the margins denticulated. Siphonal tubes 
,ong, slender, and disconnected, with simple orifices. Foot large, tongue-shaped, and 
compressed. 
This genus is closely allied to Ze//ina, differing only in the arrangement of the hinge 
furniture. In 7rzgonella the ligament is small and external, separated from the carti- 
lage, which is large, and placed in an expanded, spoon-shaped process. In Zellina 
the cartilage is invisible, or nearly so. 
1. TRIGONELLA PLANA, Da Costa. Tab. XXII, fig. 14, a—e. 
Sroonmuscie., Petiver. Gazophylacium, t. 94, fig. 3, cap. 54, 1764. 
CHAMA PIPERATA Bettonu. Aldrov. Exsang., p. 471, 1623. 
TRIGONELLA PLANA. Da Costa. Brit. Conch., p. 200, t. 13, fig. 11, 1778. 
- _ Desh. Expéd. Sci. Algérie Moll., pl. 44 to 64. 
— _- Loven. Ind. Moll. Scand., p. 45, 1846. 
— — Gray. List of Brit. Moll., p. 45, 1851. 
VENUS BOREALIS. Penn. Brit. Zool., vol. iv, p. 96, pl. 48, fig. 28. 
