CANADIAN FOSSILS. 99 



Palaeozoic Fossils in tbe Geological Museum of the University of 

 Cambridge,' 1855, but neither the characters of the genus nor of 

 the fossil are described, owing probably to the author not having 

 had time to add this description to the great work referred to. 



Cytheropsis appears to me to be a useful term for the distinction of 

 those palaeozoic Entomostraca that do not closely assimilate either to 

 Leperditia or Beyrichia, but much resemble in outline and size many 

 of the Cytheres of the existing seas, differing however from them in 

 sometimes having eye or muscle-spots, and other peculiar features, 

 such as a comparatively great thickness of the valves. Though based 

 chiefly on negative characters, this group may for the present be 

 conveniently referred to as being generic. 



I have noticed several minute Entomostraca in the Silurian rocks 

 of Wales and Sweden, which may probably belong to this group. 



VII. Cytheropsis concinna, Jones. 



(Annals of Natural History, 3d series, vol. i. p. 249, plate x. figs. 3, 4.) 



Length y\, breadth j\ inch. 



Carapace subcylindrical, tapering anteriorly ; ends rounded ; back 

 straight ; dorsal angles slightly truncate ; ventral edge of right valve 

 overlapping that of the left. Surface smooth, shining, light-brown, 

 partially pitted. In some specimens a veiy slight marginal rim is 

 traceable. 



Locality and Formation. — Many specimens, both of double and 

 single valves, in the Trenton ? limestone of Pauquette's Rapids, 

 Allumette Island, Ottawa River. 



I have had some doubt whether this may not be the young of a 

 Leperditia; but it has no eye- spot and is too narrow, young Leperditice 

 being proportionally broader than the adults. 



Collector. — Sir W. E. Logan. 



VIII. Cytheropsis siliqua, Jones. 



(Annals of Natural History, 3d series, vol, i. p. 249, plate x. fig. 6.) 



Length ^Lj breadth ■^\ inch. 



Carapace-valves long, narrow, pod-like or skiff-shaped; ends acute, 

 one much sharper and more tapering than the other ; dorsal edge long 

 and straight ; ventral edge convex ; one valve overlapping the other. 

 Smooth, shining, brown. 



