1916.] S. Kemp : Notes on Crustacea Decapoda. 3S3 



Groups I and V of Poniophilus. Ortmann ' in i8go published a 

 genealogical tree of the five genera known to him ; but the evidence 

 afforded by the pleopods leads to results directl}^ at variance with 

 those which he obtained and it will be well therefore to discuss the 

 matter briefly. 



The two most primitive groups of species in the family are in 

 all probability Aegean and Pontophilus, Group I. The}'' possess — 

 most of them at an^^ rate — a rudimentary exopod on the first legs, 

 the number of branchiae is at least as great as that in an}' other 

 genus and the endopod of the last four pairs of pleopods is well 

 developed and possesses an appendix interna. In Aegean the 

 seconcf leg is larger than in Pontophilus, Group I, agreeing more 

 nearly with that of Group V, and the former genus also possesses 

 a rather larger number of branchiae than the latter. In this last 

 feature it appears to be the more primitive of the two^ but in 

 the curious C-shaped form of its gills it presents a character not 

 known in any other genus of Caridea. Aegean, in my opinion, 

 must be regarded as an offshoot of the original stock from which 

 tlie other genera are descended. 



The evolution of the remaining genera of Crangonidae can, I 

 think, be traced back to Pontophilus, from which there have been 

 tvi'o main lines of descent, originating respectively in Group I and 

 in Group V. 



In Group I of Pontophilus, as lias already been noted, the 

 second leg is shorter than in the other groups and it is not difficult 

 to understand how Sabinea, Ou-en, and Paracrangon, Dana, have 

 arisen from it b}' successive steps. In Sabinea the pleopods are 

 as well developed as in any species of Group I and possess a con- 

 spicuous appendix interna ; the second leg has, however, under- 

 gone further reduction ; it is smaller than in any species of Ponto- 

 philus and terminates simph", the chela being altogether sup- 

 pressed. Paracrangon is apparenth' a further development on the 

 same line. The second legs are entirely absent and the endoi^od 

 in the last four pairs of pleopods, though large and well- formed, is 

 without appendix interna. 



The other line of development has apparently arisen through 

 forms similar to those of Group Y and terminates in four branches, 

 rejjresenting respectiveh' the genera Crangan, ly., Sclerocrangon, 

 Sars, Argis, Kroyer {=Nectocrangon, Brandt) and Prionocrangon, 

 Wood-Mason. In all these genera the endopod of the last four 

 pleopods is greatly reduced, possesses a well marked basal segment, 

 and is devoid of appendix interna. 



The evidence aft'orded by the development of the second leg 

 is, in this case, rather difficult to interpret. In all the four genera 

 named above it has a proportionately greater length than in any 

 species of Pontophilus', in Prionocrangon, evidently a very highly 

 specialised form, it terminates simply, while in the other three it 

 is chelate. But it must be presumed that all Crangonidae have 



I Ortmann, Zool. Jalirh., Syst., V, p. 530 (1890). 



