THE TERTIARY FORMATION. 11 



Genus — Cypris, Midler. {Monoculus, Auci prior.) 



Animal swimming and creeping ; inhabiting fresh water : eye single (coalesced) : 

 both pairs of antennae plumed. Carapace more or less oblong, generally smooth and 

 more or less setigerous ; occasionally punctate ; contact-margins thin and trenchant, 

 furnished on the anterior, ventral, and posterior borders with an internal lamellar 

 plate which projects freely and obliquely into the cavity of the valves, and is broadest 

 at the anterior end of the valves ; the edge of the right valve received within that of 

 the left : dorsal edge simple ; its central third (and sometimes more) slightly thickened, 

 and more or less distinctly defined by an anterior and a posterior angle ; these angles 

 in general faintly project, the central portion of the margin between them being 

 straight or slightly incurved : the ventral margin of each valve has its central portion 

 somewhat incurved. 



[Sub-genus — Cypria, Zenker} 1854. {Cypris, Auct.) 



Animal like Cypris, but having a broader eye, more slender limbs with longer setae 

 (hence greater briskness of motion in swimming), a peculiar bag-like prolongation of 

 the mucous gland in the male genital apparatus, longer and thinner spermatozoa, and 

 a bending downwards of the ovary at first between the valves instead of upwards. 

 Carapace like that of Cypris. (This includes, according to Zenker, C. punctata, Jurine, 

 C. Joanna, Baird, C. vidua, Midler, C. semilunaris (?), S. Fischer, and C. ovum, Jurine.) 



1 Zenker has studied the anatomy of Cypris and Cy there with great care, and has published the result 

 of his researches in considerable detail (' Arcbiv fur Naturgeschichte,' 1854). Besides pointing out important 

 distinctions in the limbs, shell-structure, chitine-skeleton, and eyes of these minute animals (and herein 

 adding some valuable information to what has been before observed), he lays great stress on the structure 

 of the alimentary and generative organs, and on the form of the spermatozoa, as characteristic of genera 

 and species ; and, although he has on these points accumulated a great mass of observations, both novel 

 and important, yet he rightly intimates that the field is still open to investigators. His sub-genus Cypria 

 and new genus Cyprois, mainly founded on peculiarities of internal structure, are introduced here to render 

 the treatment of the subject more complete ; although, for the purposes of the palaeontologist, as I have 

 already noticed, the distinction of these, and even of Candona, from Cypris is scarcely advantageous. 

 Indeed, were it not that some of the fossil forms have been recognised in the recent state, and their generic 

 characters in consequence definitely known, it would not be always practicable to decide to what divisions 

 of the Cyprince the several carapaces really belong. 



