Fossil Cypridinidas and some Allied Ostracoda. 335 



and has been gradually losing ground since that time, until 

 it has in our days come to be almost swamped by the smaller, 

 hardier, and doubtless also more prolific species of the families 

 Cypridffi and Cytheridre, animals evidently of much more 

 plastic organization, and more capable of adaptation to 

 varied conditions of environment." (Zoology of the Voyage 

 of H. M.S. ' Challenger.'— Part III. Rsport on the Ostracoda. 

 By G. Stewardson Brady, M.D., F.L.S. 1880. Pp. 151, 

 152.) 



A full catalogue of the then known thirty-two species of 

 five genera (Ci/pn'dina, Bradi/cinetus, EurypyluSj Philomedes, 

 and Asterope), with references and synonyms, are given at 

 pages 152-154 ; and descriptions of four new species, including 

 one of a new genus [Crossophorus), follow, with illustrations. 



Thus we see that Cypridina is the type of a special group 

 of Ostracods living in the open sea, some crawling on the 

 sea-bed and some swimming free and coming to the surface 

 mostly at night ("crepuscular" in habit). Their bivalve 

 test is usually larger than those of the Cyprids and Gytherids, 

 often globose, or, at least, oval and tumid. A few fossil 

 forms are known in the Tertiary and Chalk formations ; but 

 in some of the Palaeozoic rocks Cypridince and their relatives 

 abound, making np the mass of the Carboniferous Limestone 

 at some places (as in the Isle of Man, Lanarkshire, Bolland, 

 Tenby, Cork, Belgium, and elsewhere), just as much as 

 smaller Entomostraca constitute the mass of some Silurian 

 limestones (Malvern, Sweden, Russia) and other limestones of 

 Mesozoic age (at Mountfield in Sussex, Swanage in Dorset), 

 and especially some Carboniferous Oil-shales in Lanarkshire. 



Necessarily there remains to the geologist only the hard 

 portion of the structure of these little Crustaceans, such as 

 the bivalve carapace or its separate moieties, all the locomo- 

 tive and branchial limbs and maxillary apparatus having 

 disappeared. He cannot therefore follow the zoologist closely 

 or decidedly in the detailed study of Cypridina and its allies. 

 The shape (outlines and contours) of the carapace and its 

 valves, and occasionally its ornamentation and its muscle- 

 spot, become his chief guides in the discrimination of 

 differences. 



Since, however, bivalve tests recognizable as more or less 

 closely resembling those of Cypridina remain in the strata, it 

 is evident that they should subserve as far as possible in the 

 characterization of the geological formation to which they 

 belong. Efforts made in this direction have resulted in the 

 recognition of numerous generic forms which can be referred 

 to that sroup of the Ostracoda which is known as the 



