314 MANUAL OF THE MOLLUSCA. 



1 1 in each valve ; ligament external, prominent ; pallial sinus deep, hori- 

 zontal. 



Animal with the mantle fringed; siphons short and thick, diverging, 

 anal orifice denticulated, branchial with pinnate cirri; foot very large, 

 pointed, sharp-edged, projected quite in front ; gills ample, recumbent, outer 

 shortest ; palpi small, pointed. 



Distr. 45 sp. % Norway, Baltic, Black Sea, all tropical seas. In 

 sands near low- water mark ( 8 fms.) buried an inch or two beneath the 

 surface. 



Fossil, 30 sp. Eocene . U. States, Europe. 



Sub-genera. ? Ampkick&na, Phil. A. Kindermanni, California. Shell 

 oblong, nearly equilateral, gaping at each end ; teeth f ; ligament external, 

 pallial line sinuated. 



fyhigenia, Schum. (Capsa, Lam. 1818, not 1801. Donacina, Fer.) 

 1. Brasiliensis, PL XXI. fig. 20. Shell nearly equilateral, smooth; hinge- 

 teeth 2.2, one bifid, the other minute ; laterals remote, obsolete in the left 

 valve : margins smooth. Distr. 4 sp. W. Indies, Brazil, W. Africa, Pacific, 

 Central America. Inhabits estuaries; I. ventricosa, Desh. is rayed like 

 Galatea, and has its beaks eroded. 



? Isodonta (Deshayesii) Buv. Bull. Soc. Geol. Oxf, Trance. 

 GALATEA, Brliguiere. 



Si/n. Egeria, Roissy. Potamophila, Sby. Megadesma, Bowdich. 



Type, G. reclusa, PL XXI. fig. 21. 



Shell very thick, trigonal, wedge-shaped ; epidermis smooth, olive ; um- 

 bones eroded ; hinge thick, teeth 1.2, laterals indistinct ; ligament external, 

 prominent ; pallial sinus distinct. 



Animal with the mantle open in front ; siphons moderate, with 68 

 lines of cilia, orifices fringed ; foot large, compressed ; palpi long, triangular; 

 gills unequal, united to the base of the siphons, the external pair divided 

 into 2 nearly equal areas by a longitudinal furrow, indicating their line of 

 attachment. 



Distr. 2 or 7 sp. ? Nile, and rivers of W. Africa. 



FAMILY XVII. SOLENID^. 



Shell elongated, gaping at the ends; ligament external; hinge-teeth 

 usually 2.3, compressed, the posterior bifid. External shell layer with defi- 

 nite cell- structure, consisting of long prisms, very oblique to the surface, and 

 exhibiting nuclei ; inner layer nearly homogeneous. 



Animal with a very large and powerful foot, more or less cylindrical : 

 siphons short and united (in the typical Solens, with long shells) or longer 

 and partly separate (in the shorter and more compressed genera) ; gills 

 narrow, prolonged into the branchial siphon. 



