MOILUSCA. SIPHONIDA. 409 



A A. Shape various. 



a. Ligament internal. 



b. Inequivalve. CoRBULADiTi. 

 Corbula. 

 bh. Equivalve. Mactradje. 

 c. Ligament simple. 

 d. Lateral teeth. 

 Mactra. 

 Goodallia. 

 Lepton. 

 KelHa. 



d d. No lateral teeth. 

 Loripes. 

 Ervillia. 

 c c. A subsidiary external ligament. 

 Amphidesma. 

 a a. Ligament external. 



b. Two primary teeth, at most, on the same valve. {Nyni' 

 phaces of Lamark.) 

 c. Ligament at the shortest side, being the poste- 

 rior one abbreviated. Donacid^. 

 Donax. 

 Capsa. 

 Tellina. 



c c. Ligament at the longest side. 

 d. No lateral teeth. 

 Psammobia. 

 Astarte. 

 d d. Lateral teeth. 

 Lucina. 

 Myrtea. 

 b b. Three teeth, at least, on the same valve ; the other 

 with an equal number, or less. {Conques of Lamark.) 



c. Marine. Venerid^e. 

 Cyprina. 

 Cytherea. 

 Venus. 

 Venerupis. 



c.c. Fluviatile. Cycj^ahje. 

 Cyclas. 

 Cyrena. 

 (Galateola.) 



IV. Cloak closed ventrally ; the anteal opening small, and not 

 exposing the mouth or gills, and serving as a passage for 

 the foot ; posterior openings tubular. 



A. Lodged at the extremity of a calcareous tube with which 

 it is more or less irdimately connected. Tekedinid;e. 

 Teredo. 

 Xylophaga. 

 Fistulana. 

 Clavagella. 



