1922.) S. Kemp: Notes on Crustacea Decapoda. 115 



sion that has prevailed, it may be mentioned that Balss has recently 

 redescribed the type species of Periclimenes as a new form of 

 Urocaris and that a single species has been described by Schenkel, 

 Nobili, Lenz and Miss Rathbun — all writers of experience — under 

 the names Ancylocaris brevicarpalis, Palaemonella aberrans, Harpi- 

 liiis latirostris and Periclimenes hermitensis respectively. 



Borradaile's recent system of classification does little to re- 

 move the sources of error. The primary divisions in his synoptic 

 key to the genera depend almost wholly upon habit of body. This 

 character appears to me to possess little generic importance and, 

 inasmuch as the subfamily comprises species with every imaginable 

 gradation of form, between the most slender and the stoutest, it 

 is frequently quite impossible to decide on the section to which any 

 particular form should be allocated. 



I have attempted in this paper to devise a more workable 

 arrangement. In so doing I have been led to discard Urocaris, 

 Ancylocaris and Periclimenacus as distinct genera and to merge 

 all the species belonging to them, together with those of Borra- 

 daile's subgenera Falciger, Cristiger, Comiger and Hamiger under the 

 single name Periclimenes. The large assemblage of species thus 

 constituted is divided into three subgenera, Periclimenes , Pericli- 

 menaeus and Ancylocaris, which together comprise the majority of 

 known species of the subfamily. Except for Harpiliopsis, which is 

 no doubt identical with Harpilitis, the remaining genera retain 

 their rank; several, however, are inadequately described and one 

 or two may even prove not to belong to the subfamily. 



Whether the new grouping in the Periclimenes section demon- 

 strates the real affinities of the species better than the old one is 

 a question on which it is difficult to express a decided opinion. It 

 is clear from the manner in which they are combined that many 

 of the characters which are used in the distinction of species must 

 necessarily be convergent in origin and it is impossible to be certain 

 that this is not also the case with some of those to which I have at- 

 tached generic or subgeneric significance. The new grouping, how- 

 ever, removes some of the obvious anomalies that have hitherto 

 existed and will, I believe, be found convenient in practice. In 

 proposing this new scheme of classification it will be understood 

 that I disagree with much that Borradaile has said regarding the 

 phylogeny of the group and that my views on the way in which the 

 different genera have originated differ very widely from those 

 which he has illustrated in the form of a phylogenetic tree. 



The Pontoniinae are for the most part Indo-Pacific in distri- 

 bution and the subfamily is almost exclusively marine. The only 

 exceptions to the latter statement are Periclimenes indicus, P. 

 demani and P. obscurus, which frequent lagoons of variable salinity 

 on the eastern side of the Indian Peninsula. The two former 

 species are capable of enduring extreme alterations in salinity and 

 both have been found in water that is quite fresh as well as in 

 pure sea-water. Periclimenes obscurus has been found both in 

 the sea and in brackish water. The members of the subfamily 



