708 MR. W. T. CALMAN ON MACETJEOFS [May 16, 



In C. wycJcii * and O. typus I find the following arrangement : — 



This agrees with the formula for Atya. Clans states that 

 Troglocaris lacks the arthrobranch of the first perseopod. According 

 to Boas, Atyaephyra desmarestii has no arthrobranch on the first 

 perseopod, and only one on the third maxilliped. 



The males are usually somewhat smaller than the females, and 

 have as usual the pleural plates of the abdomen less deep. In the 

 female the two flagella of the antenuule are of about equal length, 

 and about twice as long as the peduncle, the outer flagellum 

 being slightly thickened for about two-thirds of its length. In the 

 male both flagella are much elongated, the outer being longer than 

 the inner, and in uninjured specimens measuring more than four 

 times the length of the peduncle, or about one-half the length of 

 the body. The thickened basal part is more distinct than in the 

 female. I have not observed any sexual differences in the arma- 

 ture of the walking-legs or of the maxillipeds, nor in the shape of 

 the anterior margin of the carapace, such as are described by 

 Miiller in Atyoida. 



The eggs carried by the females are ovoid in form, measuring 

 about •18x'27 mm. 



Total length of largest specimen ( $ ), 23 mm. 



Many specimens of this form were collected in shallow water. 



Comparing the new form with the other genera of Atyidce as 

 revised by Ortmann (Proc. Acad. Nat. 8c. Philad. 1894, p. 397), 

 we find that (like all the other higher Atyidce) it differs from Xiplio- 

 cans, Troglocaris, and Atyaepliyra in the absence of exopods from 

 all the perseopods. It resembles Caridina and difiers from Atya 

 and Atyoida in the fact that the- carpus of the second perseopods 



* The formula given by Hickson is incomplete (Ann. Mag. Nat. Hist. (6) ii. 

 1888, p. 361). Although the number of the epipods (mastigobranchiffl) is given 

 correctly, these organs appear to have escaped his notice, for he figures as 

 " mastigobranchiffi " the long oosal seta; of the perteopods. The true ejiipods are 

 of a shape similar to those of many other Caridca, and like those figured by Joly 

 in Atyaephyra and by Miiller in Atyoida, consisting of a short curved stem 

 directed backward and terminated by a strong hook wliich grasps firmly the 

 coxal setie of the next suceerling peraeopod. 



t It is possible that one of these should be regarded as a pleurobranch. In 

 Atya the corresponding gills are certainly arthrobrauchs, as stated by Pocock 

 (A. M. N. H. (6) iii. 1889, p. 15). Claus, who does not attach much 

 morphological importance to the place of insertion, assigns these two gills to 

 his series h k c respectively (Neue Beitr. z. Morph. d. Crust., Arb, Zool. Ingt. 

 Wien, vi. 1884, p. 57). 



