DECArODA. 377 



before in heiTing fishing, I found in every one of them several of these 

 ci'abs ■which had been brought up in the nets, and not one of any other 

 species. 



Leach remarks that " P. arcnatiis differs from P. emarci'matus only 

 in the form of the anterior part of the shell, and may be no more than a 

 variety of that species." M. Edwards considers them the same. All the 

 specimens preserved (about thirty) from the different localities mention- 

 ed, — and there is about an equal number of both sexes ranging fi-om a 

 very small size up to that of Leach's figure of P. cman/inattis, — have 

 the anterior part of the shell corresponding to that of P. nrciuitiis, or 

 in other words, arched : — " fronte arcuato integro " is Leach's descrip- 

 tion of it. 



Gemis PoLYBlus. 

 P. Hensloivii, Leach.' • 



A crab of this species was obtained at Crook Haven, County Cork, in the 

 month of August by ] )r. Allman, who kindly sent it to me. It M'as remarked 

 at the same time by its captor that the species appears to be " eminently 

 natatory," and that " the one taken was swimming Avith great ease near 

 the surface of the water among shoals of Acalcp/icp." It would appear, 

 from the general work of Milne Edwards on the Crustacea, that this is 

 the only species of its genus known. It was described by Leach from 

 specimens taken on the coast of Devonshire, and is given by ]M. Edwards 

 as one of the species of La INIanche, these being the only localities no- 

 ticed for it in the two works. 



Genus Pinnotheres. 

 P. Pisum, Leach. 



Templeton has noticed this species as " dredged up in Belfast Lough." 

 It is commonly found in Modiolus vulgaris on the Irish coast, where it is 

 of much more frequent occurrence than in the locality in which Dr. 

 Leach endeavoured to ascertain the number found in a certain quantity 

 of mussels. In the article Crustaceology (Edin. Ency.) it is remarked 

 that — " in one hundred of Mi/tilus modiolus, Dr. Leach found three of 

 this species." On opening eighteen specimens of the Modiolus ruff/aris 

 of various size — the produce of dredging off Bangor (Co. Down) in 

 October, 183-5 — I found fourteen individuals of P. Pisum, all females : in 

 one shell only two of the crabs occurred. I have subsequently opened 

 quantities of these Modioli Avith similar results as to the number of the 

 Pinnotheres, but in all other instances more crabs Averc obtained from a 

 like number of shells in consequence of more of the Modioli producing 

 two of them. 



The smallest Pinnotheres I have seen was found by ]Mr. Hyndman in a 

 living Cardium exiguum dredged by us in Strangford Lough in Oct., 

 1834. It is a male: the carapace is under a line in length ; the entire 

 breadth of the crab from the extremities of the outstretched legs is 3 

 lines.* The Cardium is under 3 lines in length, and barely exceeds that 

 admeasurement in breadth, so that the era!) when in tlic ])osition just 

 mentioned must have on both sides touched the walls of its chosen prison. 

 The Pinnotheres likewise inhabits the Cardium edule. Before me is one 



* In the Eiituinolos'i-"il Magazine, vol. iii., the Zovn cif tliis Viniiolheres is 

 described and ligurcd by Mr. J. V. Thompson. 



