200 
CRUSTACEA. 
ridges ; the last caudal segment or intermediate portion forming an 
elongated triangle*. 
Sometimes the four anterior feet, or the two first and one of the 
second f are terminated by two elongated fingers, forming a complete 
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 magin ; 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 trans- 
versal, and forms a common body with the forcejjs ; 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 
mediate 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 
Axius, Leach, 
Differs from Callianassa in the claws, which are nearly equal, and 
in the carpus, which does not form part of the forceps ; the posterior 
feet are similar to the preceding ones, The leaflets of the lateral 
fins are nearly equal in size, and have each a longitudinal ridge. 
The filaments of the mediate antennae are evidently longer than their 
peduncle. The 
Axim siirhj/nchus, Leach, Malac. Brit., XXXIII, is found 
on the coast of England, and on that of the western departments 
of France, Avhere it Avas obseiwed by hi. d’Orbigny, sen., a cor- 
responding member of the Mus. d’Hist. Nat. 
Our second and last subdivision consists of Crustacea Avhose six 
anterior feet form as many cIraa's, terminating in a perfectly didac- 
tyle forceps, a character Avhich distinguishes them from all the pre- 
ceding Decapoda, and one Avhich approximates them to the first of 
the ensuing section ; but here the cIraa’s of the third pair are the 
largest, Avhereas there, it is the tAvo first, besides Avhich they are much 
thicker. The peduncle of the lateral antennae is accompanied by a 
scale or spine. The external leaflet of the lateral fins at the end of 
the tail, in all the living species, is divided in two by a transverse 
suture;|; In the 
* Thalassina scorjiionides, Ij'iit. •, Cancer anontalus, Ilerbst., LXII ; Lcadi, Zool., 
Miscel., eXXX ; Desraar., Consiil., XXXYI. 
•j' The left claw of the second pair seems to be monodactyle in the Callianassee, 
and the penultimate joint dilated into a palette. 
X This character is common to the following section, so that by it Ave might 
divide the Macroura, the Schizopoda e.xcepted, into two great divisions. 
