Rev. A. M. Norman on Recent EryonticUe. 177 



single distal spine on meros, carpus, and manus ; lower 

 margin of manus spinulated, edge of finger minutely and 

 exquisitely serrated. Last pereiopods much smaller than the 

 others, chelate, the finger longer than the thumb. First 

 pleopods with the terminal portion styliform. Length 50 

 millims. 



Male taken off Portuguese coast in 220 fathoms, ' Porcu- 

 pine ' Exped. 1870, Station 13, lat. 40° 16' N., long. 9° 37' W. ; 

 female in 257 fathoms (Station 8, lat. 48° 13' N., long. 

 9° 11' W.) on the Channel slope. 



Now these two crustaceans show a very close resemblance 

 to each other in all general characters, while the points of 

 divergence are only such as might reasonably be expected to 

 result from difference of sex and of size ; and I cannot feel 

 myself justified in regarding them as belonging to two species j 

 and still less am I prepared to place them in two genera. 

 The female is much smaller than the male ; and this fact and 

 the difference of sex may well account for the less-pronounced 

 character of the spinous adornment of the carapace in the 

 former : it will be observed that the arrangement of the lines 

 of spines is the same in both. I have gone into very minute 

 detail as to the number of spines which compose the rows, 

 because it is only here that any difference can be detected ; 

 but no species- splitter has yet gone so far as to base character 

 on such minutia? as these. The male before us, indeed, 

 proves from its own carapace that stress must not be laid 

 on such points ; for while one lateral margin has seven spines 

 on the hepatic region, the other has eight. The one important 

 point of distinction between the two ' Porcupine ' Polycheles 

 is the character of the last pereiopods. Is, then, the achelate 

 or chelate structure of these limbs a difference resulting from 

 genus or sex ? 



3. Sexual diversity in the last pereiopods of the male is a 

 common feature among the Crustacea. 



The male sexual organs are situated at the base of the last 

 pereiopods; and while many organs, both of the cephalothorax 

 and pleon, undergo frequently the most remarkable modifica- 

 tions, as indirectly subservient to the sexual functions, in few 

 organs are these modifications more general or more remark- 

 able than in the last pereiopods. Many instances might be 

 cited among the higher Crustacea, while among the Copcpoda 

 the varied and peculiar modifications of these limbs in the 

 male are found to be of no small importance in the diagnosis 

 both of genera and of species. 



i. Male Crustacea arc constantly found to differ from their 

 females by structural differences which : in the aggregate, are far 



