Palaeozoic Bivalved Entomostraca. 249 



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 distinc- 

 tion of those palseozoic Entomostraca that do not closely assimi- 

 late either to Leper ditia or Beyrichia, but much resemble in 

 outline and size many of the Cytheres of the existing seas, differ- 

 ing however from them in sometimes having eye- or muscle- spots, 

 and other peculiar features, such as a comparatively great thick- 

 ness of the valves. Though based chiefly on negative charac- 

 ters, yet 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. 



6. Cytheropsis concinna, spec. nov. PI. X. figs. 3, 4. 



Length -^j, breadth -^^ 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-brow^n, partially pitted. In some specimens a very slight 

 marginal rim is traceable. 



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 

 Leperditics being proportionally broader than the adults. 



7. Cytheropsis Siliqua, spec. nov. PI. X. fig. 6. 



Length ■^■^, 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. 



Two separate valves of this curious and rather obscure form 

 (so much resembling Bairdia Siliqua of the Chalk, and the 

 recent B. Minna) occurred in the limestone from Pauquette^s 

 Rapids. 



8. Cytheropsis rugosa, spec. nov. PI. X. fig. 5. 



Length Jj^, breadth ^^ inch. 



Small, c(mvex, subreniform, broad, rounded at both ends, 



