412 Prof. T. R. Jones and Dr. H. B. HoU on the 



horn-like projections at the anterior third reaching further out 

 than those behind. 



The small specimen (fig. 13), though smooth and having 

 the antero-ventral tubercle undeveloped, is sufficiently like 

 the foregoing to be regarded as a young form or an arrested 

 dwarf. This specimen (from bed no. 37?) has been lost. 



P. cornuta is represented by a unique carapace in the A^ine 

 Collection, xxxv, bed no. 40. 



We connect this and the two following species with Fri- 

 mifia, regarding the tubercles as representing essentially the 

 elevated sides of the modified dorsal furrow. 



18. Pnmitia cequalis^ sp. nov. 



(PL XIV. figs. \la,llb.) 



Proportions : — L. 16. H. 9. Th. 5, and between the tips 6. 



This is Leperditioid in shape, and like P. vaJida^ var. angas- 

 tatttj in lateral aspect, but differing in dorsal outline. It has 

 two equal, prominent, rounded tubercles in the middle-dorsal 

 region, almost in a line, marking off thirds of the length, and 

 connected below by a feebly-raised loop-like ridge, curving 

 over the centre of the valve. Tlie dorsal aspect is narrow- 

 ovate, with the four outstanding tubercles symmetrically dis- 

 posed in fore and aft pairs. The surface is finely reticulated, 

 and the hinge-line delicately denticidate. 



Smith Coll., no. 37, railway-cutting, Coalbrook Dale ; and 

 no. 38, railway-cutting, side of Severn, Ironbridge. Rare. 



This species reminds us of P. hicornis, Jones (Ann. & 

 Mag. Nat. Hist. ser. 2, vol. xvi. p. 173, 1855, pi. vi. fig. 23), 

 from the Lower Silurian ; but, besides other differences, the 

 proportionsof the latter are: L. 18-75. H. 9'25. Th. 9-25. 

 The faint loop, evidently a family link with Bollia, Placen- 

 tula^ and Strepida^ serves to show that the centro-dorsal 

 sulcus is not quite obsolete in these cornute Prhnitue. It is 

 more definitely marked in the allied P. hicornis and P. mun- 

 dula^ Jones [pp. cit. figs, 23, 28-31). 



19. Primitia diversa, sp, nov. 



(PL XIV. figs. 10 a, 10/^, 10<!.) 



Proportions : — L. 14. H. 1. Th. 6, and between the tips 8. 



Valves straight-backed, Leperditioid, and subconvex. Sur- 

 face finely reticulated or marked with small scattered pits ; 

 irregularly undulate, and rising into two unequal tubercles, 

 one near the middle of the front third, the other low down on 

 the hinder third. Dorsal view of the closed carapace narrow- 

 ovate, with lateral, projecting, unequal tubercles. 



In the Vine Collection xxxvii,2, 3, and xxxvii, bed no. 37; 

 also LXIY; Buildwas Beds. Rather common. 



