BIVALVIA. 



235 



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 Tettina. 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. 



Tettina tennis is enumerated in Mr. Smith's ' List of the Clyde Fossils/ 



TRIGONELLA. Da Costa. 1778. 



SPOONMUSSEL. Petiver. 

 MACTRA (sp.) Gmelin. 

 MYA (sp.) Chemn. 

 TELLINA (sp.) Donov, 

 LIGULA (sp.) Mont. 1808. 

 SOLEN (sp.) Olivi. 

 ARENARIA. Megerle. 1811. 

 SCROBICULARIA. Schumacher. 1817. 



LAVIGNON. Cuv. 1817. 



LUTRARIA (sp.) Lam. 1818. Swains. 1840. 



LISTERA. Turt. 1822. 



LUTRICOLA. Blainv. 1824. 



AMPHIDESMA (sp.) Flem. 1828. 



CALCINELLA. Agass. 1842. 



SEMELE (sp.) Woodw. 1854. 



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 

 iong, slender, and disconnected, with simple orifices. Foot large, tongue-shaped, and 

 compressed. 



This genus is closely allied to Tellina, differing only in the arrangement of the hinge 

 furniture. In Trigonella the ligament is small and external, separated from the carti- 

 lage, which is large, and placed in an expanded, spoon-shaped process. In Tettina 

 the cartilage is invisible, or nearly so. 



1. TRIGONELLA PLAN A, Da Costa. Tab. XXII, fig. 14, a c. 



SPOONMUSCLE. Petiver. Gazophylacium, t. 94, fig. 3, cap. 54, 1764. 

 CHAMA PIPERATA BELLONII. Aldrov. Exsang., p. 471, 1623. 

 TRIGONELLA PLANA. Da Costa. Brit. Conch., p. 200, t. 13, fig. 11, 1778. 



Desk. Expe'd. Sci. Alg^rie Moll., pi. 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, pi. 48, fig. 28. 



