ORDER DECAPOA. 177 



venous sinuses of which we have spoken in the generalities of 

 the order, there exists a third, lodged in the sternal canal, 

 and extending between the two preceding, from one end of 

 the thorax to the other. This very curious disposition would 

 establish, according to them, a connexion between the ve- 

 nous system of the macroura, and that of the stomapod Crus- 

 tacea. 



The macroura never quit the water, and with the exception 

 of a small number are all marine. 



After the example of Degeer and Gronovius, but a single 

 genus has been formed of them, that of Astacus, which we 

 shall thus divide. 



Some, from the proportions, form, and uses of their feet, of 

 which the first or second at least, are in the form of claws, 

 and from the sub-caudal situation of their eggs, evidently ap- 

 proximate to the preceding Crustacea, and still more to those 

 which are vulgarly known under the names of craw-jish^ lob- 

 ster, and prawn or shrimp. 



The others have very slender feet in the form of a thread 

 or lash, and accompanied with an appendage or external and 

 elongated branch, which seems to double their number. 

 They are proper for swimming, and none of them terminates 

 in a forceps. The eggs are situated between them, and not 

 under the tail. 



The first shall be subdivided into four sections, the Ano- 

 mala, LocusTiE, AsTACiNi, and Carides. 



The second shall compose the fifth and last section of this 

 family and of the decapods, that of Schizopoda. 



In the first, or that of Anomala, the two or four last feet 

 are always much smaller than the preceding. The under 

 part of the tail never presents more than four pair of appen- 

 dages, or false feet. The lateral fins of the end of the tail, or 

 the pieces which represent them, are thrown on the sides, and 

 do not form with the last segment a fin, in the form of a fan. 



VOL. XIII. N 



