404 Prof. T. R. Jones and Dr. H. B. Holl on the 



Mag. Nat. Hist, ser, 5, vol. xv. p. 189) they assimilate, 

 though they want the usual subcentral pit. K. rigida, J. & 

 K., I. c. fig. 18, is also such a pitless form, and may belong 

 to the same group as these Silurian allies of Kirkhya. K. 

 fihula {op. cit. ser. 4, vol. iii. pi. xv. fig. 9, p. 224), from the 

 Upper-Ludlow beds near Malvern, holds its own as a species 

 of this genus. 



The quasi-Kirkbyan specimens here noticed may be grouped 

 under the new generic name of Strepula *. 



The carapace-valves are slightly convex, suboblong, with 

 rounded ends, or semielliptical, that is, less boldly curved at 

 one end than at the other, and bear narrow often trenchant 

 ridges. These are sometimes concentric with the lower mar- 

 gin, in other cases partly concentric and partly irregular. 

 They run into the slightly thickened dorsal margin. The 

 intervening furrows form broad valleys and a subcentral 

 tubercle, or even a lobular swelling is sometimes present. 

 The chief ridge is a free supramarginal lamina, standing 

 outwards and downwards, and hiding the real marginal edge 

 in the side view. The edge view of the bivalved carajDace is 

 narrow-ovate, cross-barred at the sides with ridges, some 

 straight and parallel, some oblique and divergent (PL XIII. 

 figs. 8 5, 9 ^'). 



1. Strepula concentrica, sp. nov. 

 (PI. XIII. figs. \a,lb, 4, 6.) 



r Fig. 1: Length 12. Height?. Thickness 5. 

 Proportions! : \ Fig. 4 : Length 19. Height 9. 

 (Fig. 6: Length 24. Height 11. 



Three concentric but not quite symmetrical narrow ridges 

 are here present (including the supramarginal lamina), some- 

 times showing a tendency to " sport " or branch, and even to 

 have a connecting isthmus here and there. A small central 

 tubercle is seen in fig. 1 a. 



This species occurs in Mr. Smithes collection: — no. llg, 

 Lincoln Hill, Ironbridge ; no. 42, railway-cutting, side of 

 Severn, Ironbridge ; and no. SSs, Woolhope. 



2. Strepula irregularis, sp. nov. 



(PI. XIII. figs. 5,7,8a,Sb,9a.,9b,d c, and 15.) 



-D . /Fig. 8: L. 20. H. 12. Th. 10. 



Proportions : | ^.-^ ^ . j^ 34. H. 12. Th. 10. 



* Diminutive of Strepa (Lat.), a stirrup, from tlie loop-like pattern of 

 the ridges. 



t If these proportioual numbers be divided by 15, the results will be 

 measurements in a millimetre and parts of a millimetre. 



