LAMAECK'S GENEEA OF SHELLS. 



ARRANGED ACCORDING TO THE DESCENDING SCALE, WITH 

 THE ADDITION OP SOME RECENTLY FORMED GENERA. 



TESTACEOUS MOLLUSCA. 



Animals soft, inarticulated, provided -mth an anterior 

 head, which is more or less projecting, or salient ; most 

 frequently furnished with eyes and tentacula, or sometimes 

 having arms disposed in the form of a coronet ; their mouth 

 short, elongated, or tubular, extensile and usually armed 

 with hard parts. Mantle diversified, having its edges free 

 on the sides of the body, or the lobes united, forming a sac 

 or bag, which partly envelopes the animal; gills or organs 

 of respiration various, rarely symmetrical; circulation double, 

 one partial, the other general ; heart unilocular, sometimes 

 with the auricles separated, and very distant, no continuous 

 medullary cord along the body, but a few scattered nerves 

 and ganglions ; body sometimes naked, either unprovided 

 with solid internal parts, or enclosing a shell or other hard 

 substance ; but generally provided with an external shell 

 covering the body, or sheathed in it, and which is never 

 composed of two opposite valves. 



ORDER I-HETEROPODA. 



Head distinct, with two eyes, but destitute of arms 

 arranged around the head ; body free elongated, fitted for 

 r3 



