140 Scientific Intelligence. 



with the Leucosidea, although these are far more nearly allied to the 

 Calappidce, not having the afferent canal covered by the exognath of 

 the outer inaxillipeds, which is the case in all Leucosidea. 



Again, Dr. S. remarks, "The genus Grapsus, limited by the rejection 

 of Leptograpsus, Metopograpsus, etc., and represented by the species 

 Pharaonis, strigosus, Webbi, etc., must be removed not only out of the 

 Grapsoidea, but even entirely out of the Brachyura, because the struc- 

 ture of the external antennae differs completely from that which prevails 

 amongst the Brachyura. Grapsus, for instance, has no operculum at the 

 base of the external antenaB, but a perforated tubercle, as in the Macroura, 

 and must therefore at least be placed among the Anomoura." Here we 

 would have Leptograpsus variegatus and Grapsus strigosus. for instance. — 

 forms so closely allied that they are placed in one and the same genus 

 by so skillful a naturalist as Dana. — separated so widely from each other 

 that the latter species is placed among the Anomoura! Let us examine 

 fresh or wet specimens to ascertain whether Grapsus in reality has, at 

 the base of the antennae, a structure so essentially differing from that 

 found in ordinary Brachyura. Dried specimens are too commonly used 

 in these investigations, and are very apt to lead to error. The " oper- 

 culum," spoken of above, is the coxal joint (coxocerite) of the external 

 antennae, which is moveable in all crabs, even where the next (basicerite) 

 is not. In a Ma'm for example, this coxal joint may be raised a little, 

 so that the membranous areola, 1 which occupies its postero-interior 

 surface, may be partially seen. In Leptograpsus this areola is more ex- 

 posed, encrOachiog somewhat upon the margin or outer surface of the 

 coxal joint, or, in other words, this joint is kept permanently a little 

 raised. In Orapeus the coxa) joint (here the "perforated tubercle" of 

 Strahl) is still more evolved, and its sides are folded in, giving it a 

 globular form, and contracting the areola, which is thus placed in a slit 

 and becomes almost wholly externa). The different form of the coxo- 

 cerite in Grapaua is, therefore, the result of a simple modification, not 

 of structural importance. In iJromia the coxal joint is also slit, at one 

 side, but the areola is on the inner surface. This joint in Dromia is not 

 "so shrunken that only the tubercle remains." It is far larger in pro- 

 portion than is usual in the higher Crustacea. Dr. Strahl says that "if 

 we imagine the slit in the tubercle of Dramia carried out to one side, 

 so that here the peripheral margin is completely separated, we have the 

 operculum of the Brachyura in it- perfect form." But this prolongation 

 of the slit would cut the coxal joint in two, which is not the case in the 

 "operculum." For this "operculum" is truly the homologue of the 

 coxocerite of Dramia and ffemorus in its entirety ; as may be seen by 

 comparing with this part in Pilunutus, for instance, where the basicerite is 

 not soldered t<> the contiguous parts as is usual in Cancroids, but is free 

 and articulated directly with the "operculum" in the same manner as it 

 is with the coxal joint in the other two genera named. Pilumnus, we 

 may remark incidentally, would be classed with Parthenope by the char- 

 acter of its antennae. 



1 The so-called tympanum. It is very doubtful whether the auditory organ is 

 ever here situated. Kroyer has demonstrated (Kongl. Danske Vidensk. Sehkabs 

 Skrifter, 1S56, iv, 288) that a far more complicated auditory apparatus exists at the 

 base of the internal antenna?. 



