On the Palaeozoic Bivalved Entomostraca. 211 



XXX. — Notes on the Palceozoic Bivalved Entomostraca. No. IX. 

 Some Silurian Species. By Prof. T. Rupekt Jones, F.Gr.S., 

 and Dr. H. B. Holl, F.G.S. 



[Plates XIV. & XV.] 



The specimens about to be described were obtained mostly 

 from the calcareous bands of the Woolhope and Wenlock strata 

 near Malvern ; and, having for the most part retained their 

 shells, they afford better materials for the determination of 

 species than many of the small Bivalved Entomostraca ob- 

 tained elsewhere from the Silurian rocks. Some of the well- 

 preserved Silurian Entomostraca found in the neighbourhood 

 of Malvern have been already sorted out and described by us 

 as Primitice, in the ' Annals of Nat. Hist.' ser. 3. vol. xvi. 

 pp. 414-425. 



[The measurements of the specimens described are given in 

 a Table at p. 227.] 



1. Cy there corbidoides, sp. nov. PI. XV. figs. 4a-4e, 

 figs. 5 a, b. 



Carapace somewhat egg-shaped, swollen posteriorly, inequi- 

 valved, subtriaugular in every aspect. Sometimes the right 

 valve and sometimes the left is larger than the other. In 

 fig. 4 c the left valve is more convex in its upper portion than 

 the other, rising far above it at the dorsal margin ; and the 

 right valve has an oblong outline in side view, with rounded 

 ends. In other specimens, as in fig. 4 a, the right valve is 

 large and high. The outline of the larger valve forms a sca- 

 lene triangle with the upper angle replaced by a bold curve, 

 and the lateral (terminal) angles, especially the anterior corner, 

 less rounded : thus the ventral margin is flattish and the back 

 highly arched, with a steeper downward slope backwards than 

 forwards. Some specimens occur in which there is less in- 

 equality of the valves, but the left valve seems usually the 

 larger one. 



The hinge-line is straight, about two-thirds the length of 

 the valve, is overhung by the umbo-like convexity of the 

 larger valve, and in the smaller valve its middle third is 

 accompanied by a narrow parallel depression. The ventral 

 margin of each valve is sometimes slightly lipped at the pos- 

 terior angle (fig. 4 d). 



The ventral profile of the carapace is broadly ovate, with 

 the narrow end suddenly sharp ; the end view (fig. 4 e) is 

 broadly cordate, with the apex upwards. 



