Palceozoic Bivalced Entomostnica. 413 



20. Primitia semmulum, Jones. 

 (PI. XIV. figs. 14 a, 14 ^>, 14 c.) 



£eyrtchut semimilmn, Jones, Aim. & Mag. Nat. Hist. ser. 2, vol. xvi. 



1855, p. 173, pi. vi. fig. 24. 

 Pi'imitia semimdum, J. & H., op. cit. ser. 8, vol. xvi. I860, p. 418. 



f Fig. Ua,h: . . L. 17. H. 10. Th. 8. 

 Proportions: \ Fig. 14c: .... L. 14. H. 9. 



(Figured in 1855 : L. 1875. H. 11-25. 



The original description of this pretty little semicircular 

 Primitia needs to be supplemented only by the remarks, that 

 the present specimens are clearly and elegantly reticulated ; 

 that the dorsal sulcus traverses rather more than a third of the 

 height of the valve and is not always quite straight ; and, 

 lastly, that the individuals vary in relative length. Fig. 14 c 

 is the outline of a short valve. 



Smith Coll. no. 26, railway-cutting, side of Severn, Iron- 

 bridge (worn) ; no. 35, Lincoln Hill, Ironbridge ; no. 54, 

 Woolhope ; no. 74, Wren's Nest, Dudley ; no. 75, Benthall 

 Edge. An abundant species. 



21. Primitia f areata J sp. no v. 

 (PL XIV. figs. 15 a, 15 6.) 



Proportions :— L. 19. H. 9. Tli. 8. 



This unique carapace is skift-shaped, with a straiglit back 

 and elliptical lower margin, which curves up sharply behind, 

 and much more gently and slopingly to the projecting antero- 

 dorsal angle. The valves are fully convex in the hinder two 

 thirds, but are compressed in front. The surface is smo(5th, 

 and impressed at the middle of the back with a well-marked 

 sulcus, which widens out into a shallow fork at about the 

 middle of the valve. A neat rim borders the free edge. Dorsal 

 view subovate, acute in front, straight at the sides, and 

 roundly truncate behind. The valves remaining slightly 

 apart in the figured specimen give a slightly deeper outline 

 in fig. 15 a at first sight than is real. 



Smith Coll. no. 43, Dudley Tunnel. 



EXPLANATION OF THE PLATES. 



[The figures are magnified about 15 diameters.] 

 Plate XIIL 



Fiy. 1. Streinda concentrica, gen. et sp. nov. Carapace: a, lateral view, 

 left valve outwards ; b, dorsal view. Smith Coll. no. 42, rail- 

 way-cutting, side of Severn, Ironbridge. 



Fig. 2. Strepula he)/ricJu'(ndi'.'i, s-p. nov. Right valve. Smith Coll. no. 11 4, 

 Lincoln Hill, Ironbridge. 



Fiff. 3. The same. Right valve. Smith Coll. no, II3, Lincoln Hill, 

 Ironbrid":e. 



