12 G. O. SARS. M.-N. Kl. 



Gen. : CeriodapJmia, Dana. 



4. CerJoda,phnia Rigaudi, Richard. 

 (PI. 2, figs. 9—15.) 



Cci'iodapJmia Rigandi, Richard, Sur quelques animaux inférieurs des 

 eaux douces du Tonkin. Mém. Soc. Zool. de France, T. VII, 

 p. 239. 



Specific Characters. Carapace of female rather tumid, seen laterally, 

 rounded quadrangular, posterior projection short, and occurring above the 

 longitudinal axis; that of male narrower, with the dorsal margin straight, 

 and the ventral slightly sinuated. Head in both sexes much depressed, 

 procumbent, being defined dorsally by a deep depression, front rounded 

 and slightly projecting, inferior part produced to a very acute, deflexed 

 rostrum; fornix simple, without any projecting corner. Surface of shell 

 distinctly reticulated all over with rather large hexagonal meshes, free 

 edges of the valves smooth. Eye of moderate size ; ocellus small, puncti- 

 form. Antennulae in female not extending to the tip of the rostrum, 

 oblong fusiform, with a rather long sensory bristle anteriorly; those in 

 male considerably larger, projecting far beyond the rostrum, and having 

 a distinct setiform flagellum. Tail in female with the dorsal processes 

 very small, terminal part rather narrow, and nearly of uniform breadth 

 throughout, being obliquely rounded at the tip, anal denticles only 6 on 

 each side; terminal claws quite smooth; caudal setæ rather elongate. 

 Body semipellucid, of a pale orange colour, changing to light reddish. 

 Length of adult female 0,55 mm., of male 0.38 mm. 



Remarks. This form was first described from Tonkin by M. J. 

 Richard, and subsequently recorded by the same author from another 

 locality; but no figures have ever been given of the species. The most 

 prominent character is undoubtedly the acute rostral projection, for which 

 reason I at first noticed the species under the provisional name of C. avi- 

 rostris. It agrees in this respect with the C. cornuta, described by the 

 author from Australia; but this species has besides an acute horn-shaped 

 projection on the front, not found in the present form. Two other spe- 

 cies have been recorded as being likewise provided with a rostral pro- 

 jection, viz., C. textilis Dana and C. asperata Moniez, but these species 

 would seem to differ in other respects from that here treated of. 



Description of the female. 



Fully adult, ovigerous specimens but little exceed in length V2 mm., 

 and this form accordingly belongs to the smaller species of the genus. 



