Palaozoic Bwalved Entomostraca. 249 



nor of the fossil are described, owing probably to the .'inthor not 

 liiiviiig had time to iuld this description to the great work 

 referred to. 



('ijtlicropsis a])i)cars to me to be a useful term for the distinc- 

 tion of those palaeozoic Entomostraca that do not closely assimi- 

 late either to Lepei-ditia or Beyrichin, 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 pecidiar features, such as a comparatively great thick- 

 ness of the valves. Though based chietiy 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. Cytkeropsis concinna, spec. nov. PI. 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 ovcrla])ping that of the left. Surface smooth, shining, 

 light-brown, 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 Lcperditia ; but it has no eye- spot and is too narrow, young 

 Leperditia being proportionally broader than the adults. 



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



Length jVj 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 Bnirdia Siliqua of the Chalk, and the 

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

 Rapids. 



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



Length ^^, breadth t^'t^ inch. 



Small, convex, subrcniform. broad, rounded at both ends. 



