1899.] 



CRUSTACEAN'S TROil LAKE TAKGjUSYIKA. 



70^ 



respectively, while the dactylus of the fifth pair was half as long 

 again and had a row of 39 spines. 



In the female, the first pair of pleopods (PI. XL. fig. 14) 

 have the endopod rather slender, pointed, and more than half the 

 length of the exopod. In the male (PI. XL. fig. 15), the endopod 

 is a short ovate leaflet about one-quarter the length of the exopod. 

 In nearly all the specimens of both sexes the first pair of pleopods 

 are turned forward, witli the exopod lying above and external to 

 the bases of the posterior perseopods. According to F, Miiller 

 (Kosmos, ix. 1881, p. 121), this is the position taken by these 

 appendages in the living Ati/oida, and he states that they serve to 

 protect the entrance to the branchial chamber, the fringe of 

 marginal setae acting as a sieve to exclude mud, &c. 



In the second pleopods of the male (PI. XL. figs. 17, 17ci), the 

 appendix masculina is a little shorter than the appendix interna, 

 and bears a number of stout spines. 



The telson (PI. XL. fig. 18), is about as long as the inner plates 

 of the uropods, with straight sides, tapering to the obtusely pointed 

 tip which bears four spines, two short external and two longer 

 internal, between which latter spring three plumose setae. On the 

 dorsal surface of the telson are two pairs of spinules. In C. wychii 

 the tip of the telson bears eight spines, and the dorsal surface three 

 pairs of spinules. 



The gills are four in number on either side, three pleurobranchs, 

 corresponding to the second, third, and fourth peraeopods, and 

 one which I believe to be a pleurobranch (though it is difficult to 

 determine the precise point of insertion) aboAe the first peraeopod. 

 There are no epipods on the maxillipeds or peraeopods, unless we 

 regard as a rudimentary epipod the small papilla at the base 

 of the third maxilliped described above. In tabular form the 

 arrangement is : — 



The statements of various authors as to the branchial formulas of 

 the genera of Atyidce are somewhat conflicting, but all agree in 

 giving a larger number of gills and a complete series of epipods as 

 far as the fourth peraeopods.* 



* F. Miiller states {I. c. p. 121) that in Atyoida potimirim. the last two pairs 

 of legs are without epipods. 



