790 W. T. OALMAN. 



of tlio West Indian Islands has the same branchial formula 

 as Caridella and Afcyella, and in fact only differs from 

 the last-named genus in having chehe of a distinctly Atya 

 type. He refers the West Indian species to a new genus, to 

 which he gives the name Calm an ia. He supposes it to 

 have been derived from Atyella in the same way as Atya 

 from Ortmannia, and he concludes that Atyella (and 

 Caridella also) must formerly have existed in America. 

 From this view I would venture to dissent. Even if the 

 phenomena of mutation lead us to believe that similar forms 

 of chelipeds may have been acquired independently in 

 different localities, there is no greater difficulty in supposing 

 that a simple suppression of the posterior plcurobranch may 

 also have occurred more than once iti the evolution of the 

 family. In all the groups of animals composing the remark- 

 able fauna of Tanganyika, there is reason to believe that 

 many of the endemic genera and species have been differen- 

 tiated within the limits of the lake itself; and until the 

 Atyida; with a reduced branchial formula are shown to 

 have a much wider geographical distribution than is at 

 present known, it seems impossible to believe in a direct 

 affinity between the Tanganyikan Atyella and the West 

 Indian Cal mania. 



It may be freely admitted that these phylogenetic specula- 

 tions rest upon much less solid ground than do the conclusions 

 drawn directly from experiment or based upon statistics; 

 but unless we are to abandon all hope of rationalising the 

 facts of systematic and geographical biology, some such 

 hypotheses are, for the present, indispensable. 



List of Papers referred to. 



Bordage, E.. '08. — " Rechevches experimeutales snr les luntations 



ovolutives de certains Crustaces de la famille des Atjida?,"" • C.R. 



Acad. Sci. Paris." cxlvii, pp. 1418-1420. fig. 

 ■ 'OOa.^'" Snr la regeneration liypotypiqne des cbelipedes chez 



Atya serrata Sp. Bate," 'C.R. Acad. Sci. Paris," cxlviii, pp. 



47-50. 



