66 CRUSTACEA. 



than the thumb or movable finger, merely constituting a simple 

 tooth. The 



Gebia, Leach, 



Approaches the preceding sub-genera in the two anterior feet 

 which are alone didactyle. The leaflets of the lateral fins of the end 

 of the tail widen from the base to their extremity, and are marked 

 with longitudinal ridges. The intermediate piece or the last seg- 

 ment of the tail is nearly square(l). 



Thalassina, Lat. 



The four anterior feet terminated by two fingers; leaflets of the 

 lateral fins of the end of the tail, narrow, elongated, and without 

 ridges; the last caudal segment or intermediate portion forming an 

 elongated triangle(2). 



Sometimes the four anterior feet, or the two first and one of the 

 second(3) are terminated by two elongated fingers, forming a com- 

 plete forceps. 



The two anterior claws are the largest; the lateral leaflets of the 

 fin terminating the tail, are in the form of a reversed triangle, or 

 widest at the posterior margin; the intermediary, on the contrary, 

 is narrowed from base to apex, and terminates in a point. 



Callianassa, Leach. 



The claws of the Callianassas are very unequal, both as to form 

 and proportion; the carpus of the largest of the two anterior ones is 

 transversal, and forms a common body with the forceps; the same 

 joint of the other claw is elongated; the two posterior feet are almost 

 didactyle. The external leaflet of the lateral fins at the end of the 

 tail is larger than the internal, and has a ridge; the latter is smooth. 

 The ocular pedicles are squamiform, and the cornea is situated 

 near the middle of their external margin. The filaments of the me- 

 diate antennae are not longer than their peduncle. 



Callianassa subterranea, Leach, Malac. Brit., XXXII, is the 

 only known species. It is found on the coasts of France and 

 England. The 



(1) Thalassina litoralis, Risso, Crust., Ill, 2; Gebia slellata, Leach, Malac. Brit., 

 xxxi, 1 9. See Desmar., Consid., p. 203, 204. 



(2) Thalassina scorpionides, Lat.; Cancer anomalus, Herbst, LXH; Leach, Zool. 

 Miscel., CXXX; Desmar., Consid., XXXVI. 



(3) The left claw of the second pair seems to be monodactyle in the Callianassx, 

 and the penultimate joint dilated into a palette. 



