CLASSinCATlON OF THE MATOIJ) CRUSTACEA. 



Gil 



tion may bo traced from Micippa with ^Yell defined orbits, to tbo 

 remarkable gcnw^ Picrocenis,\\\ wbich the true orbits arc as little 

 developed as iu many Inaehina?. 



In cases such as these, I believe it is often better to preserve 

 the natural sequence of the genera, though in so doing one must 

 slightly overstep the literal deliuitiou, than, by too strict an 

 adherence to the definition of the group, to separate forms which 

 in all characters save one may be nearly allied. Nature imposes 

 no artificial limits ; and not even an arbitrary distinction will in 

 all cases avail to separate kindred forms *. 



Legion II. Parthenopinea. (Parthenopinea, Dana et auctoriim). 

 Basal antennal joint very small, and embedded with the next joint in 

 the narrow hiatns between the front and inner suborbital angle ; the 

 infraocular space being mainly occupied by the lower wall of the 

 orbit. 



Family IV. Parthenopid/E. Characters of the section : — This group 

 corresponds in the main with M. -Edwards's Parthenopiens ; but the cha~ 

 raeters are modified to include several genera which agree with those 

 known to Milne-Edwards in the structure of the orbits and antenna?, but 

 ditfer in the carapace and auterior legs. Moreover I follow De Haan in 

 excluding Eurynome (which really belongs to the Maiidfc) and including 

 (Ethra (which is placed by Milne-Edwards in a separate section of the 

 Canceriens — Canceriens cryptopodes) . 



As already stated, tlie Parthenopinea are very distinct as a 

 group from the rest of the Oxyrhyncha. Perhaps their nearest 

 affinities in that direction are wdtli InacUus through Inaclioides. 

 The triangulate form of the carapace, with its strongly marked 

 depressions separating the different regions, is the same, and the 

 slender basal antennal joint. In Inaclioides the rostrum is simple, 

 as in Farthenope and Lamhrus. 



In the plates that accompany this paper I have figured 

 what may be regarded as typical examples of the principal 

 modifications in the structure of the orbital and antennal region 

 throughout the Oxyrhyncha, w^herein may be traced the gradual 



Dana, for example, separated the Cancroidea into two parallel groups 

 (CancridaD and Eriphiidse), characterized respectively by the presence or absence 

 of a ridge on the endostome defining the efferent branchial channel; but in 

 Xanthodius, a genus since described by Stimpson, this ridge is rudimentary, and 

 this genus may be referred either to the vicinity of Chlorodius in the former, or 

 Oziiis in the latter group. Similar intermediate forms occur between Actcea 

 and Act(Podes, genera belonging respectively to the parallel series Xanthintcand 

 Chlorodiina) in the family Cancrida;. 



48* 



