CRUSTACEA. 



67 



GENUS, PlEIMELA. 



"Carapace rounded in front, and about as wide as long, 

 strongly embossed, and toothed at the sides, the third articulation 

 of the inner foot- jaws giving insertion to the next on its in- 

 ternal edge." 



Mr. Bell defines the genus as being most easily recognised 

 from all other Canceridcc, in the circumstance that the external 

 foot- jaws are advanced over the epistome to the autennary 

 cavities. 



Pieimela denticulata. — Leach. Malac. Brit. pi. 3 ; Milne 

 ■ Edwards, Hist, des Crustacea, t 1, p. 424. 



"This is the only known species of the Genus, and is not 

 common." 



It has been taken all round our southern coast and in one or 

 two places in Ireland. It is a species that is not littoral, since it 

 is generally taken in the trawl refuse. 



PORTUNLB^E.— (Swimming Crabs.) 

 Genus, Carcinus. 

 Terminal articulations of the hindmost legs lancet shaped 

 flat and broad, carapace broader than long, front advanced. 

 Carcinus Mjenas — Common Harbour Crab. — Leach, Malac.pl. 5; 

 Pennant, pi. 2, fig. 5; Milne Edwards, Hist, des Crust, vol. 1, 

 p. 484. 



One of the commonest crabs of our shores, where it hides 

 under stones on the beach but never goes far from land. It 

 is a hardy species, easily kept in confinement for the sake of 

 observation, and has even survived the being kept in fresh 

 water. It lives in fresh water streams where the sea enters. 



The development of this crab has been observed through 

 all its stages from the zcea to the adult form, and it seems to be 

 one of progressive morphology. — (Vide Phil. Trans.) 



Genus, Portumnus. — Leach, Bell. 



" Platyonychus. — Edivards, Hist, des Crust., 

 V.l, p. 434; Couch. 

 " Hinder legs with a wide and oval joint ; corresponding part 

 of the other legs straight and unfit for swimming." 



This definition of Couch's is scarcely sufficient to determine 

 the Genus from that of Portunus. Portumnus is easily detected by 



