1922.] S. Kemp : Notes on Crustacea Decapoda. 135 



is decidedly longer than in nearly all the species referred to 

 Urocaris. 



It remains to be seen whether there are any other characters 

 which will justify the retention of Urocaris and Ancylocaris as 

 separate genera. The type of Stimpson's Urocaris is U. longicaud- 

 atus , from the West Indies. In this species, as in P scriptus (Risso), 

 the type of Costa's Periclimenes, the last three peraeopods have 

 biunguiculate dactyli. Several Indo-Pacific species are closely 

 allied to U . longicaudatus, but the latter does not possess the anten- 

 nal spine of the carapace which is present without exception in all 

 other species hitherto referred to Urocaris, Ancylocaris and Pericli- 

 menes. On the closest examination and comparison it does not 

 seem possible to separate a group of species to which the name 

 Urocaris can be applied and, if the genus is to be retained, it must 

 be monotypic and characterized solely by the absence of the an- 

 tennal spine of the carapace. It is very difficult to assess the 

 value of a unique character of this kind ; but in view of the clear 

 affinity which exists between U . longicaudatus and various other 

 species I am of the opinion that Urocaris should be regarded as a 

 synonym of Periclimenes. An illustration of the impossibility of 

 distinguishing between Urocaris and Periclimenes, as usually ap- 

 plied, is to be found in a recent paper by Balss, in which the 

 type of the latter genus is redescribed as a new species of the 

 former. 



Ancylocaris was erected by Schenkel for a species, A. brevicar- 

 palis, which is now known to be commensal with giant anemones 

 of the genus Discosoma. The same species has since been described 

 under a variety of specific names ; it was referred to the genus 

 Palaemonella by Nobili, to Harpilius by Lenz, and to Periclimenes 

 by Miss Rathbun. It will be seen from Borradaile's key that 

 Ancylocaris in reality differs from Periclimenes in only one character 

 — that the carapace of the female is strongly swollen dorsally. This 

 feature is well developed only in large females and a slight swelling 

 of the carapace is not infrequently seen in normal Periclimenes. 

 Moreover, in a species described in this paper which is also com- 

 mensal with Discosonm, the carapace is not at all swollen, though in 

 all other respects it shows an extremely close affinity wih A. brevicar- 

 palis. T here is thus clear proof that the swollen carapace of the 

 female in A. brevicarpalis is not a character of generic value. As 

 will be seen further on, the name Ancylocaris may be employed in 

 a new sense for a subgenus of Periclimenes. 



It may here be pointed out that the extent to which the outer 

 antennular flagellum is cleft — a character to which Borradaile attri- 

 butes importance — cannot be used, at any rate in the Periclimenes 

 group, for the separation of genera. In Periclimenes there is a 

 small and rather clearly defined group of species inhabiting water 

 of moderate or great depth and the four known representatives of 

 this group agree among themselves even in a peculiar disposition 

 of teeth in the second pair of chelae. In two of them (P. 

 latipollex and P. laccadivensis) the outer antennular flagellum is 



