114 Records of the Indian M useiiin. [\'oi.. \'II, 



The most conspicuously primitive feature of the genera Xipho- 

 caris and Xiphocaridina is the possession of well-formed exopods 

 on all the peraeopods, a schizopod-like character which they share 

 with one other Atjdd genus, Palaemonias, Hay, from the mam- 

 moth cave of Kentucky. In three other genera, Synicaris, Troglo- 

 caris and Atyaephya^ exopods are also found on certain thoracic 

 legs, but never on all, while they are uniformly absent from Atya, 

 Caridina and Ortmannia, genera which comprise the large majority 

 of known species of the family, and from Liinnocaridina , Caridella 

 and Atyella that constitute the peculiar Atyid fauna of lake Tan- 

 ganyika. 



Until comparatively recently the distinctions between Xipho- 

 caris and Xiphocaridina were not recognized ; but Bouvier (iqoQt?) 

 had pointed out that the West Indian X. elongata, the type of the 

 former genus, differs from its supposed congeners in New Zealand, 

 China and Australia in several important structural features. 

 He consequently created for the latter species a new genus, 

 Xiphocaridina. 



Xiphocaridina is distinguished from Xiphocaris by the pres- 

 ence of supra-orbital spines on the carapace, by the anteriorly 

 excavate carpus of the first peraeopods, by the presence of tufts 

 of hairs on the tips of the fingers of the chelae (a character found 

 in all At3ddae with the exception of Xiphocaris) and by the absence 

 of arthrobranchs at the base of the first four peraeopods. 



From a consideration of these characters it is evident that 

 Xiphocaridina has proceeded on a line of specialization similar to 

 that whcih has resulted in the evolution of Caridina and this fact 

 determined Bouvier in his choice of its name. Xiphocaris , as at 

 present understood, is the most primitive genus in the family ; except 

 for the complete suppression of the mandibular palp, it bears a 

 very close resemblance to the Hoplophoridae. 



Palaenionias, Hay (1902. p. 226), is distinguished from both 

 the preceding genera by the distal excavation of the carpus of the 

 second pair of peraeopods and by the unpigmented and non-facet- 

 ted e3^es. It appears to resemble Xiphocaris in the absence of a 

 supra-orbital spine and Xiphocaridina in the reduction of its bran- 

 chial system.' 



Up to the present time only the following species of Atyidae 

 with the full number of exopods on the thoracic limbs have been 

 described : — 



Xiphocaris elongata (Guerin). 



Cuba; Hayti ; Dominica; St. Domingo. 



Xiphocaridina cotnpressa (De Haan). 



Yokohama ; Tokio ; Flores ; Queensland ; Victoria ; 

 New vSouth Wales ; Norfolk Is. 



' Hay states (p. 229) that " the gills seem to be only four in number, on each 

 side attached to the first four peraeopods, but there may be a rudiment on the 

 fifth." In Xiphocayidina there are seven gills (one rudimentary) on either side 

 and twelve (one rudimentary) in Xiphocaris. 



