314 MANUAL OF THE MOLLUSCA. 



1 — 1 in each valve ; ligament external, prominent j iJallial 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, shaq)-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. ? Amphichmia, Phil. A. Kindermanni, California. Shell 

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

 pallial line sinuated. 



Iphiyenia, 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; /. ventricosa, Desh. is rayed like 

 Galatea, and has its beaks eroded. 



? Isodonta (Deshayesii) Buv. BuU. Soc. Geol. O.if. France. 

 Galatea, Bruguiere. 



St/n. Egeria, Roissy. Potamophila, Sby. ]Megadesma, Bowdich. 



Type, G. reclusa, PI. XXI. fig. 21. ' 



Shell very thick, trigonal, w^edge-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 6 — 8 

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

 giUs 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 XVIL Solenid^. 



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

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

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

 exhibiting nuclei ; inner layer neai'ly 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 longa- 

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

 narrow, prolonged into the branchial siphon. 



