CONCHIFERA. 271 



Shell oval or ark-shaped, compressed, smootli or concentrically furrowed, 

 epidermis olive; ligament external, elongated, prominent: hinge with an 

 anterior and posterior series of fine sharp teeth ; interior sub-nacreous ; pal- 

 lial sinus large and deep ; anterior adductor giving off a long oblique pedal line. 



Animal liice Yoldia ; mantle-margins slightly fringed and furnished with 

 ventral lobes ; siphonal tubes united, long and slender, completely retractile ; 

 palpi appendiculate, convoluted, as long as the shell ; gills narrow, posterior ; 

 foot deeply cleft, forming an oval disk, even-margined and striated across. 



Dlstr. 2 sp. Valparaiso; New Zealand (shell like S. ornata). 



Fossil, 1 sp. Miocene. Pt. Desire, Patagonia. 



? SoLEMYA, Lamarck, 



Tifpe, S. togata, PI. XXII. fig. 17. Spi. Solenomya, Menke. 



Shell elongated, cylindrical, gaping at each end ; epidermis dark, horny, 

 extending beyond the margins ; umbones posterior ; hinge edentulous ; liga- 

 ment concealed ; pallial line obscure. Outer layer of long prismatic cells, 

 nearly parallel with the surface, and mingled with dark cells, as in Finna ; 

 inner layer also cellular. 



Animal with the mantle lobes united behind, with a single siphonal orifice, 

 hour-glass shaped , and cirrated ; foot proboscidiform, truncated and fringed 

 at the end ; gills forming a single plume on each side, with the laminae free 

 to the base ; palpi long and narrow, nearly free. 



The shell resembles Glycimeris in the shortness of its posterior side, and 

 the extraordinary development of its epidermis ; the animal most resembles 

 Leda in the structure of its foot and gills. 



Distr. 4 sp. TJ. States, Canaries, W. Africa (Gaboon K.), Medit. Aus« 

 tralia, New Zealand. Burrowing in mud ; 2 fms. 



Fossil, 4 sp. Carb. — . Brit. Belgium. 



FAMILY V. Tbigoniad^. 



Shell equivalve, close, trigonal, with the umbones directed posteriorly ; 

 ligament external ; interior nacreous ; hinge-teeth few, diverging ; pallial 

 line simple. 



Animal with the mantle open ; foot long and bent ; gills two on each 

 side, recumbent ; palpi simple. 



Trigonia, Bruguiere (not Aublet.) 

 Etym. Trigonos, three-angled. Syn. Lyriodon, G. Sby. 

 Ex. T. costata, PI. XVII. fig. 24. T. pectiuata, fig. 183. 

 Shell thick, tuberculated, or ornamented with radiating or concentric 

 ribs ; posterior side angular; ligament small and prominent; hinge-teeth 2.3, 

 diverging, transvei'sely striated ; centre tooth of left valve divided ; pedal 

 impressions in front of the posterior adductor, and one in the umbo of the 

 left valve ; anterior adductor impression close to the umbo. 



