ON THE BRACHYUROUS DECAPODS OF THE CAPE. 



63 



two minute tubercles at the base of a longitudinal carina. An irregular transverse carina 

 stretches out on each side from the last lateral marginal tooth towards the middle of the shell, 

 marking out the upper limit of the branchial region. The chelse are marked above with five 

 keels on the fixed digit, and three or four longitudinal furrows on the middle finger. The 

 second, third, and fourth pair of feet, are compressed, having their third and fourth joints 

 bicarinated, and their ungues furrowed. The fifth pair of feet are less bicarinated, and the 

 last joint or claw is like the posterior claw of Carcinus mcBnas, Leach, only more broad. 

 The length is less than an inch. 



8. We now return to the aberrant family EripUdcB, by means of which we pass to Thelphusa 

 among the Grapsina. It becomes therefore necessary to point out the families of a stirps 

 which is very common in warm climates, and the study of whose manners afforded me much 

 amusement whilst I resided in the West Indies. Dr. Milne Edwards calls them Catametopes, 

 and says that some of them are " completement terrestres." This is an error, however; for all 

 these crabs must lay their eggs in water, must pass then' infant state in water, and must, 

 during their future life, return periodically to the vicinity of water. The land-crab par excel- 

 lence, Gegarcinus ruricola, Lat., in this respect, does not differ in economy from other 

 Brachyurous Decapods, nor does it retire many leagues from the sea. In our small West 

 India islands it may be found all over them ; but in Cuba it has its hmits, which are confined 

 to a certain distance from the shore. 



Stirps. GRAPSINA, or Square Crabs. 



families. 



Aberrant Groupe. 



Tigellus of external pedipalps 

 never inserted at the mid-< 

 die of the apex of third 

 joint. 



Thelphusid^, M. E. 

 Fresh Water Crabs. 



I G0N0PLACID.E, M. E. 



Deep Shore Crabs. 



> OcYPODiD^, Leach. 

 Low Shore Crabs. 



Normal Groupe. 



r 



Grapsi, Dehaan. 

 Tigellus of external pedipalps< 

 inserted at the middle of 

 the apex of third joint. 

 Palpi never dentated. 



Grapsidji, M. E. 

 Salt Water Crabs. 



Gegarcinid^, M. E. 

 True Land Crabs- 



r Ocular peduncles short. Tigellus of external pedipalps 

 <! never inserted at the outer angle of third joint. Scape 

 L of the palpi unidentated on the inside. 

 fOcular peduncles long. Tigellus of external pedipalps in- 

 <l serted at the inner angle of third joint. Scape of the 



palpi unidentated on the inside, 

 r Ocular peduncles long. Tigellus of external pedipalps al- 

 ways inserted at the outer angle of third joint. Scape 

 of the palpi not dentated. 



r Shell depressed, and the whole structure such as to render 

 I these crabs unable to retire far from the sea. 



C Shell convex in order to contain a certain quantity of water, 

 enabling these crabs to travel great distances on land. 



1 



9. Dr. Smith has brought specimens of all the above families of Grapsijia except of the 

 Gegarcinidce. The first family Thelphusidce has the genital organs of the male placed nearly 

 as in the last stirps Cancrina, with which it is osculant. But the other families of Grapsina 

 have the genital orifices of the male placed in a transverse groove hollowed out on the 

 sternum. Both the ThelphtLsidce and GonoplacidcB being aberrant famihes, agree with the 

 Cancrina in having the scape of their palpi unidentated on the inside. 



