72 On Ancient Water-fieas of the 



makes a mere crescentic slit or triangular opening in the two united 

 valves of some; but, when the valves gape in front, it makes a 

 cruciform opening; and if the notch be strongly developed, the 

 antero-dorsal portion of the carapace projects as a beak, forming 

 more or less of a hood. The muscle-spot on each valve, or place 

 of attachment of the great transverse muscle, is distinctly marked 

 with a patch of small lucid spots, sometimes having a radiate 

 arrangement. 



Milne-Edwards, Baird, Dana, Costa, Sars, Grrube, Brady, and 

 others, have treated of these forms with their soft parts ; and for 

 English readers, Dr. Baii-d's description and figures in the Zoolo- 

 gical Society's Proceedings, and G, S. Brady's illustrated memoirs 

 in the Zoological Society's Transactions, vol. v., and the Linnean 

 Society's Transactions, vol. xxvi., and his subsequent papers in the 

 Zoological Society's Proceedings, 1871, &c., will supply useful 

 particulars. 



In the fossil state there are abundant evidences of the former 

 existence of Cypridiniform Ostracods, chiefly in the Palaeozoic rocks, 

 especially the Carboniferous Limestone and the Coal-measures. As 

 indicated in my " Monograph of the Tertiary Entomostraca of 

 England " (Palseontographical Society),185(), pp. 2 and 9, the name 

 Cypridina had been misapplied by palaeontologists to fossil Cytherm, 

 in some cases, and not given to veritable members of the genus, 

 on account of the characteristic notch not having been represented 

 by the engraver in the figure of M. Milne-Edwards' Cypridina 

 Reynaudii* 



There are fossil carapace-valves so nearly corresponding with 

 those of a living Cypridina, that, as far as the valves can guide us, 

 there are no characteristics whereby to judge between one species 

 and another, except those of general shape, form of notch, amount 

 of overlap, pattern of muscle-spot, superficial ornament, and relative 

 thickness. 



Among the recent Cypridinadas themselves the limbs and other 

 soft parts supply the main data for specific valuation. Perhaps 

 Bradycinetus alone is characterized by speciality of carapace, the 

 others having valve-characters of variable and mutual modification. 

 Indeed, it is difiicult to allocate to the more definitely studied 

 genera of existing monographists all the so-called " Cypridinae " of 

 earlier authors, for want of exact information as to the soft parts of 

 the respective animals, male and female. Polycope and GytJierella, 

 which are not " Cypridinads," but belong to two allied families, 

 possess recognizable carapaces. 



As at present known, the recent Cypridinadse comprise — 1. 

 Cypridina, M.-Edwards; 2. Asterope, Philippi; 3. Fhilomedes, 



* 'Hist. Nat. des Crustaces,' vol. iii., p. 407, Plate XXXVI., Figs. 5-9; and 

 'Hist. Nat. Anim. sans Verteb.,' ed. 2, vol. v., p. 178. 



