3G2 A HISTORY OF RECENT CRUSTACEA 



the Dynamene forms have the pleon not rugose and the 

 uropods fixed some way up the terminal segment, and the 

 branches not in any marked manner extending beyond it, 

 nor separated from one another. The forms rubra and 

 viridis are also without dorsal tubercles. No one appears 

 to have ever found the Ncesa form or Dynamene Montagui 

 carrying eggs, and, as they are not at all uncommon, they 

 may, therefore, be presumed to be of the male sex. The 

 differences between the female Dynamene and Ncesa in the 

 hinder half of the animal are superficially very great, but 

 they are bridged over to a certain extent by the inter- 

 mediate form of Dynamene Montagui. All the three forms 

 agree in having both branches of the fourth and fifth pleo- 

 pods furnished with transverse folds or pleats so as to be 

 fully branchial. Dynamene in 1814 had as yet no species. 

 Cymodoce, Leach, 1814, It is not easy to understand 

 why authors have combined not only to adopt a different 

 form of this name, but to base the alteration on Leach's 

 original authority. In this genus the pleon is dorsally 

 tuberculate, with two apical notches, and the outer branch 

 of the uropods so placed that it cannot completely close 

 under the inner, both branches remaining always salient. 

 The British species are Gymodoce truncata, Leach, and 

 Cymodoce emarginata, Leach, the latter of which has not 

 recently been found. Cymodoce Lamarckii, Leach, from 

 Sicily, is briefly described, and not in agreement with the 

 generic definition. M. Eugene Hesse has persuaded him- 

 self, not only that Dynam.ene is the female of Ncesa, which 

 is possible, but that Sphceroma is the female of Cymodoce, 

 which certainly cannot be accepted on such arguments as 

 he produces. As between British species assigned to the 

 two genera, there is no resemblance of colouring worth 



o cj 



speaking of, and no community of residence, except that 

 Cymodoce is occasionally and very rarely found on some of 

 the shores that also yield Sphceroma. In Sphceroma quadri- 

 dentatum, Say, Mr. Harger has ascertained that neither 

 sex is a Cymodoce. The curious fact remains that no 

 ovigerous Cymodoce has yet been recorded. It is, perhaps, 

 still more singular that the sexual characters in this group 



