462 a coenish fauna. 



Genus, Pirimela. 



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

 strongly embossed, and tootbed at tbe sides, the tbird articulation 

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

 ternal edge." 



Mr. Bell defines tbe genus as being most easily recognised 

 from all otber CanceridcB, in tbe circumstance tbat tbe external 

 foot-jaws are advanced over tbe epistome to tbe autennary 

 cavities. 



PiRiMELA DENTicuLATA. — LeacJi. Molac. Brit. pi. 3; Milne 

 Edwards, Hist, des Crustacea, t \, p. 424. 



"Tbis is tbe only known species of tbe Grenus, and is not 

 common." 



It bas been taken all round our soutbern coast and in one or 

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

 is generally taken in tbe trawl refuse. 



POi^T^ZTTVZD^.— (Swimming Crabs.) 

 Genus, Carcinus. 



Terminal articulations of tbe bindmost legs lancet sbaped 

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

 Carcinus M^nas — Common Harbour Crab. — Leach, Malac.pl. 5 ; 

 Fennant, pi. '2;fig. 5; Milne Edwa/rds, Hist, des Crust, vol. 1, 

 p. 434. 



One of tbe commonest crabs of our sbores, wbere it bides 

 under stones on tbe beacb but never goes far from land. It 

 is a bardy species, easily kept in confinement for tbe sake of 

 observation, and bas even survived tbe being kept in fresb 

 water. It lives in fresb water streams wbere tbe sea enters. 



Tbe development of tbis crab bas been observed tbrougb 

 all its stages from tbe zoea to tbe adult form, and it seems to be 

 one of progressive morpbology. — (Vide Pbil. Trans.) 



■ Genus, Portumnus. — Leach, Bell. 



" Platyonyebus. — Ediuards, Hist, des Crust., 

 V.l, p. 434; Couch. 

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

 of tbe otber legs straigbt and unfit for swimming." 



Tbis definition of Coucb's is scarcely sufficient to determine 

 tbe Genus from tbat of Portunus. Portumnus is easily detected by 



