200 CRUSTACEA. 



ridges ; the last caudal segment or intermediate portion forming an 

 elongated triangle *. 



Sometimes the four anterior feet, or the two first arid one of the 

 second f are terminated by two elongated fingers, forming a complete 

 forceps. 



The two anterior claws are the largest ; the lateral leaflets of the 

 fin terminating the tail, are in the form of a reversed triangle, or 

 widest at the posterior magin ; the intermediary, on the contrary, is 

 narrowed from base to apex, and terminates in a point. 



CALLIANASSA, Leach. 



The claws of the Callianassse are very unequal, both as to form and 

 proportion ; the carpus of the largest of the two anterior ones is trans- 

 versal, and forms a common body with the forceps ; the same joint of 

 the other claw is elongated ; the two posterior feet are almost didactyle. 

 The external leaflet of the lateral fins at the end of the tail is larger 

 than the internal, and has a ridge; the latter is smooth. 



The ocular pedicles are squamiform, and the cornea is situated 

 near the middle of their external margin. The filaments of the 

 mediate antennae are not longer than their peduncle. 



Callianassa subterranea, Leach, Malac. Brit., XXXII, is the 

 only known species. It is found on the coasts of France and 

 England. The 



Axius, Leach, 



Differs from Callianassa in the claws, which are nearly equal, and 

 in the carpus, which does not form part of the forceps ; the posterior 

 feet are similar to the preceding ones, The leaflets of the lateral 

 fins are nearly equal in size, and have each a longitudinal ridge. 

 The filaments of the mediate antennae are evidently longer than their 

 peduncle. The 



Axius stirhynchus. Leach, Malac. Brit., XXXIII, is found 

 on the coast of England, and on that of the western departments 

 of France, where it was observed by M. d'Orbigny, sen., a cor- 

 responding member of the Mus. d'Hist. Nat. 



Our second and last subdivision consists of Crustacea whose six 

 anterior feet form as many claws, terminating in a perfectly didac- 

 tyle forceps, a character which distinguishes them from all the pre- 

 ceding Decapoda, and one which approximates them to the first of 

 the ensuing section ; but here the claws of the third pair are the 

 largest, whereas there, it is the two first, besides which they are much 

 thicker. The peduncle of the lateral antennae is accompanied by a 

 scale or spine. The external leaflet of the lateral fins at the end of 

 the tail, in all the living species, is divided in two by a transverse 

 suturej In the 



* Thalassina scorpionides, Lat. ; Cancer anomalus, Herbst., LXII ; Leach, Zool., 

 Miscel., CXXX ; Desmur., Consid., XXXVI. 



f The left claw of the second pair seems to be monodactyle in the Callianassae, 

 and the penultimate joint dilated into a palette. 



t This character is common to the following section, so that by it we might 

 divide the Macroura, the Schizopoda excepted, into two great divisions. 



