30 CEYLON PEAEL OYSTER REPORT. 



names. Nescea, Leach, has priority, but is preoccupied. Ncesa was substituted for it. 

 But Dynamene has priority over Ncesa, although its title is a little peculiar. It 

 was indeed defined in advance of the substituted naming of Ncesa, but the species for 

 which it was defined were not specified by name until 1818. The simplest issue out 

 of the complication seems to be by reducing the two genera and their four repre- 

 sentative species to a single genus and species under the name Dynamene bidentata 

 (Adams). Thus Ncesa disappears, and Dynamene in its place acquires an intelligible 

 status. 



The relief, however, is not very great, because there are several other species that 

 have been assigned to this dimorphic genus before its dimorphism was understood, 

 and of these the true generic position remains uncertain. 



Although sexual dimorphism is not conspicuous in SphcBroma, Exosplueroma, or 

 Parasphceroma, in many other genera of the family it has been more or less clearly 

 established, and there exists at least a possibility that the females of different genera 

 may be nmch less divergent in appearance than the males. The latter sex is dis- 

 tinguished in Dynamene and Campecopea by having the sixth segment of the perseon 

 dorsally produced, in Zuzara, Cycloidura, Isocladus, and Hasivellia by having the 

 perseon's seventh segment so produced. In Dynamene, Campecopea, Ciliccea, and 

 Noesicopea the males have the inner ramus of the uropods degraded (with an exception 

 subsequently mentioned). In Ancinus that ramus is wanting, but the sexes have 

 not as yet been discriminated either in that genus or in Tecticeps, which shows a 

 near relationship to it. The uropods in Tecticeps are biramose, with the inner branch 

 much the shorter. 



In regard to some isolated members of the family, it may be suggested that 

 Sphceroma algoense, Stebbing, 1875, Cymodocella tubicauda, Pfeffer, 1887, and 

 Splueroma (?) egregia, Chilton, 1891, must all belong to the same genus, and may 

 possibly deserve to be united under the name Cymodocella algoensis. Cymodocea 

 antarctica, Hodgson, 1902, also appears to approach Cymodocella more nearly than 

 Cymodoce. Exosphceroma amplifrons, Stebbing, would, according to my present 

 view, stand better in the genus Cymodoce, and, in any case, I agree with my friend 

 Dr. H. J. Hansen that it cannot properlv be retained under Exosplueroma. 



Since the above was written, Mr. Holmes has kindly sent me his interesting essay 

 on the sexes of Sphseromids (' Proc. California Ac. Sci.,' ser. 3, Zool., vol. 3, p. 295). 

 He takes the view that the name Dynamene should be accepted in place of Ncesa, 

 hut further extends it to supersede Ciliccea, a procedure which can scarcely be 

 accepted without more consideration and argument. As regards the male sex, 

 Cymodoce seems fairly distinguishable by superficial characters from Dynamene and 

 both sections of Ciliccea, but whether there are stable and sufficient marks for 

 separating either the female or the juvenile forms of Cymodoce and Ciliccea in all 

 cases is less clear. The addition of new species without tolerably full description and 

 figures is rather to be deprecated than welcomed. 



