REPORT ON THE CRUSTACEA MACRURA. 293 



mastigobranchia, one arthrobranchial and one pleurobranchial plume, but no basecpbysis. 

 The penultimate pair carries the rudiment of an arthrobranchial plume in the form of a 

 small papilla, and one well developed pleurobranchia. The posterior pair is stout, short, 

 and carries no mastigobranchia, plume, nor basecpbysis. On the ventral surface, between 

 the fourth pair, a large sharp tooth, flat and broad at the base, lies directed anteriorly and 

 reaches as far as the second pair, and between the fifth or jaosterior pair in the male the 

 foramen for the passage of the vas deferens, instead of being situated on the coxa, is 

 placed on the ventral portion of the last somite of the pereion. 



The pleopoda are all single-branched and very short ; the anterior pair in the male is 

 furnished with a petasma that is cincinnulated in the median line. 



The second pair has the inner branch developed in the form of a petasma of a some- 

 what less pronounced condition than that of the first pair. The other pairs are simple, 

 and the posterior forms the lateral plates of the rhipidura. 



The branchial arrangement is shown in the following table : — 



Pleurobrancbiae, 

 Artbrobrancbise, 

 Podobranchiffi, 

 Mastigobrancbiae, 



This genus was described by Milne-Edwards in 1830, and embraced three species, 

 Sicyonia sculpta, Milne-Edwards, from the Mediterranean, Sicyonia carinata (OHvier), 

 from Rio Janeiro, and Sicyonia lancifer (Olivier). He describes the genus as being very 

 near to Penseus, which it resembles in the compressed form of the body, in the termina- 

 tion of the first pair of antennae, in the didactylous hands possessed by the first three 

 pairs of legs, in the conformation of the pleopoda and in other details. But it differs 

 most essentially in the structural character of the branchiae, in the absence of any traces 

 of pleurobranchiae, in the reduction of the arthrobranchial plumes, and in the presence of 

 one podobranchial plume attached to the first pair of gnathopoda ; the branchiae divide 

 as in Penseus, but instead of being filamentous they are foliaceous in structure, and 

 thus approximate to the condition seen in Gennadas and Sergestes. 



Geographical Distribution. — In the Challenger collection there are four species ; one 

 from the West Inches, which I take to be closely allied to Sicyonia carinata, from which 

 it differs in what may be only sexual features ; one from Torres Strait, that closely 

 resembles the figure of Hippolyte cristatus, de Haan, from the Japanese Seas, and coin- 

 cides with the description of Sicyonia lancifer (Olivier), the habitat of which is stated 

 to be the Indian Ocean ; and the third is from the north side of New Guinea. This, 

 together with the type, Sicyonia sculpta, that was taken in the Bay of Naples, and one 

 described by Stimpson from the Chinese seas under the specific name of Sicyonia 

 ocellata, gives the geographical distribution of this genus exceptional interest. 



