LAMARCK. 533 



(1) Animals attached to marine bodies. 



* No peculiar systems formed by the disposition of the 

 animals in the common mass which they inhabit. 



(a) A single opening (or mouth or anus) apparent exter- 

 nally for each individual. 

 Aplidium. Eucoelium. 



Synoicum. 



(b) Two openings (a mouth and vent) apparent 

 externally for each individual. 

 Sigillina. Distomus. 



** Animals forming peculiar isolated systems by their dis- 

 position in the common mass which they inhabit. 



(a) Animals arranged in several concentric circles 

 occupying the common mass. 



Diazoma. 



(6) Animals forming peculiar scattered systems, and 

 arranged in each system around a central cavity. 

 Polyclinum. Polycyclus. 



Botryllus. 



(2) Animals floating ivith their common mass in the bosom 

 of the sea. 



Pyrosoma. 



Order II. TUNICIERS LIBRES ou ASCIDIENS. Animals 

 separate, either isolated or clustered, but without mutual 

 communication, and not forming a compound mass. 

 Salpa. Ascidia. 



Bipapillaria. Mammaria. 



Class CONCHIFERA. (July, 1818.) 



Order I. CONCHIFERES DIMYAIRES. There are at least two 

 adductor muscles, the impressions ,of which on the inner 

 surface of the valves are separate and lateral. 

 (1) Shell regular, and generally equivalve. 

 (a) Shell in general gaping at the sides when the valves 

 are closed. 



* Conchiferes crassipedes. Lobes of the mantle entirely 

 or partially coalescent in front ; foot thick and pos- 

 terior ; gape of the shell often considerable and 

 always more or less marked. 



Les Tubicolees. Les Pholadaires. 



Les Solenacees. Les Myaires. 



** Conchiferes tenuipedes. Lobes of the mantle scarcely 

 or not at all united in front ; foot small and com- 

 pressed ; gape of the shell often inconsiderable. 

 f Ligament internal, with or without the complication 

 of an external ligament. 



