OCR Text |
Show 66 CRUSTACEA. than the thumb or movable finger, merely constituting a simple tooth. The GEBIA, Leach, Appro ches the preceding sub-genera in the two anterior feet which nre 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 segment of the tail is nearly square(!). TnALASSINA, 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). ometimes the four anterior feet, or the two first and one of the second(->) are terminated by two elongated fingers, forming a com~ plete forceps. The t o anterior claws are the largest; the lateral leaflets of the fin terminating the tail, are in the form of a reversed triangle, or idest at the posterior margin; the intermediary, on the contrary, is narro\Ted ft·om base to apex, and terminates in a point. CALLIANASsA, Leach. The claw of the Callianassre are very unequal, both as to form and proportion· the carpus of the largest of the two anterior ones is tr ·ersal nd forms a common body with the forceps; the same "oi t of the other claw is elongated; the two posterior feet are almost di ctyle. The e.xternal leaflet of the lateral fins at the end of the a."l i 1 r r th n the internal, and has a ridge; the latter is smooth. T e. ocu r pedicles are squamiform, and the cornea is situated ar tb iddle of their external margin. The filaments of the me-te re not longer than their peduncle. a ubltrrauea, Leach, Malac. Brit., XXXII, is the pe ie . It is found on the coasts of France a;d The C11 'Ffial.irJJsi1UJ. li'tora.i~:J. · • · • Cru t..III, .. ;-{;(bia ~ttllota, Le.sch, c. Brit., L• 1-9 ee sma.r. C id., P· 0'\ ~ . ('Jl Tfutlu:IIitM 11curpion:£rk3. l..&t.; Gtntetr CIJUJmalu. Herb ~ LXII; Leach, Zool. ·eeL. XXX;: : sm.ar id. .·v1. (3) '£he left c.fu.w of the 3ec p.ili mo e c · z, d the penul.tiinu.te joln.t dila.ted io.t DECAPOD A. 67 Axms, Leach, Differs from Callianassa in the claws, which are nearly equal, ~nd in the carpus, which does not form part of the forceps; the postenor feet are similar to the preceding ones. The leaflet~ of. the l~teral fins arc nearly equal in size, and have. each a long1tudmal ridg~. The filaments of the mediate antennre are evidently longer than their peduncle. The . .flxius stir!Lynchus, Leach, Malac. Brit., XXXIII, IS found on the coast of England, and on that of the weste~n departments of France, where it was observed by M. d'Ot·bxgny, sen., a corresponding member of the Mus. d'Hist. Nat. . Our second and last subdivision consists of Crustacea whose SIX anterior feet form as many claws, terminating in a perfectly didactyle forceps, a character which distinguishes them from all the preceding Decapoda and one which approximates them to the first of the ensuing secti~n • but here the claws of the third pair are the largest whereas th~re it is the two first, besides which they are much t'h icker. The pe' duncle of the lateral antennre . . d lS accompame by a scale or spines. The external leaflet of the lateral fins at the end of the tail, in all the living species, is divided in two by a transver e suture( 1 ). In the ERYON, Desmar., All the leaflets of the caudal fin are narrowed at their extremity and terminate in a point; the external one presents no transverse suture. The two filaments of the mediate antennre are very short, and hardly longer than their peduncle. The sides of the shell are deeply emarginated. The forceps of the two anterior claws are narrow an~ elong~ted. This subgenus was established by Desmarest on a foss.ll specles,Eryon Cuvieri, Hist. Nat. des Crust. Foss., X, 4; Cons1d. X~XIV, 3, found in a lithographic, calcareous stone from Pappenhe1m and Aichtedt in the margraviate of Anspach. AsTAous, Gronov ., Fa b. Leaflets of the lateral fins at the end of the tail widened and refUnded at their extremity; the external one divided transversely by a suture, and the posterior extremity of the mediate obtuse or (1) This character is com n to the following section, so that by it we might divide the Macroura, the Schizopoda excepted, into two grea~ divisions. |