DECAPODA. 23 



versely truncated before, and where the tail of the males (the only- 

 sex known) consists of seven distinct segments. Such'is the 



Orythyia, Fabr. 



The only species known, Orith. mamillaris, Fabr., Cancer 

 bimaculatus, Hcrbst., XVIII, 101, is found in the sea of China, 

 or at least forms a part of the collections of Insects sold by its 

 inhabitants to foreigners. The ocular pedicles are longer in 

 proportion than those of the Portuni. 

 The shell of the last swimmers is much wider before than behind, 

 forming either the segment of a circle narrowed towards the tail 

 and truncated, or a trapezium, or is almost in the shape of a heart. 

 Its greatest transverse diameter generally surpasses the opposite 

 one. There are but five segments in the tail of the males, instead 

 of the seven found in that of the females, the number usually pecu- 

 liar to the tail of the Decapoda; the third and the two following 

 ones are confounded or form but one; frequently, however, traces of 

 them are discovered, at least on the sides. 



We will first separate those whose eyes are supported by very long 

 and slender pedicles, arising from the middle of the anterior margin 

 of the shell, extending to its lateral angles, and received into a 

 groove run under the edge. Such is the 



Podophthalmus, Lam., 



Where the shell forms a transverse trapezium, wider and straight 

 before with a long spiniform tooth behind the ocular cavities. The 

 claws are elongated, spiny, and similar to those of most of the spe- 

 cies of the genus Lupa, Leach. 



The only living species known(l) inhabits the coasts of the 

 Isle of France and those of the neighbouring seas. 



The valuable cabinet of one of the most learned fossil con- 

 chylidogists of Europe, contains an internal cast of a fossil Po- 

 dophthalmus, to which M. Desmarest has affixed the name of 

 its possessor, M. de France(2). 

 The ocular pedicles of the other Crustacea, belonging to this sec- 

 tion, are short, occupy but a very small portion of the transverse 

 diameter of the shell, are placed in oval cavities, and resemble, 

 generally, those of the ordinary Crabs with which these swimmers 



(1) Podophthalmus spinosus, Latr., Gener. Crust, et Insect., I, 1, and II, 1; 

 Leach, Zool., Miscell. cxlviii; Portunus vigil, Fab. 



(2) Hist. Nat. des Crust. Foss., V, 6, 7, 8. 



