1903.] 



METAMORPHOSES OF DECAPOD CRUSTACEANS. 



29 



C.fasciatibs cannot be separated generically as a larva from 

 the other species named. A characteristic of the gToup to which 

 it belongs is the paired arrangement of the abdominal spines. It 

 is true that they are practically absent in C. trispmosus, but their 

 occasional appearance on one segment shows that their loss is a 

 recent one. Classifying therefore on the basis of the larval form, 

 we must merge the genus Cheraphilus into J^geon, leaving 

 the genus Pontophilus to include P. spinosus and P. norvegicus. 



This arrangement seems to fit the adults as well as it does the 

 larvae. In the first place, Ortmann seems to have made an error in 

 including all the above-mentioned forms in a single genus 

 Pontophilus. He gives as characters of this genus " GiUs seven ; 

 six pleurobranchs {i, k, I, m, n, o), and one rudimentary podo- 

 branch h " ; but I have found the following gill-formula to hold 

 for Cheraphilus trispinosus, C. nanus, and ^PJgeon fasciatzts : — 



In Pontophihcs spinosus there are seven gills, there being a 

 podobranch upon the second maxillipede. 



If this statement holds good for the remaining species, then the 

 two genera Cheraphilus and JEgeon shovild be separated from 

 Pontophilus. As regards their relation to one another, the only 

 important difierences between them seem to lie in the shape of 

 the rostrum and the direction of the bend of the apices of the 

 gills (Spence Bate). Such difierences do not seem to me of 

 sufiicient importance to allow of generic distinction, and I have 

 therefore in the heading of this paper treated the two species 

 dealt with as both belonging to the genus JSgeon Risso. 



Literature referred to in the foregoing paper . 



Bate, 0. Spence. — Report on the Crustacea Macrura collected 



during the ' Challenger' Expedition. 1888. 

 Claus, C. — Zur Kenntniss der Kreislaufsorgane der Schizoj)oden 



und Decapoden. Arb. Zool. Inst. Wien, v.. pp. 271-318 (1884). 

 Claus, C. — Zur Kenntniss der Malacostracenlarven. Wiii-zb. 



Naturwiss. Zeits. ii. pp. 23-46 (1861). 



