On the PalcBOzoic Bwalved Entomostraca. 211 



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

 Some Silurian Species. By Prof. T.RuPERT JONES,F.G.S., 

 and Dr. li. 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 fomid in the neighbourhood 

 of Malvern have been already sorted out and described by us 

 as Primitiff, 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 corhuloideSj sp. nov. PI. XY. figs. 4:a-4e, 

 figs. 5 a, h. 



Carapace somewhat egg-shaped, swollen posteriorly, inequi- 

 valved, subtriangular 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 romided 

 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 Avith the upper angle replaced by a bold carve, 

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

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

 highly arched, Avitli 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 hj a naiTOW parallel depression. The ventral 

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

 terior angle (fig. 4^7). 



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. 



