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



and front lobes take up a large portion of the surface, 

 leaving the middle lobe small, but distinct, in a subcentral 

 depression. Ventral margin slightly developed. The surface 

 bears small scattered tubercles, as in Salter's fig. 14 a, from 

 which it slightly diifers in shape, being longer in proportion. 

 Edge view narrow-oval. 



In shape and the position of the middle lobe, this form has 

 Bome resemblance to B. impendens, Jones*, but it is suffici- 

 ently distinct in several respects. 



In the " vShales over the Wenlock Limestone," no. 46. 

 This small subvar. of tuherculata, Salter, has a " very limited 

 range in the Shales " (Vine). 



(8) Beyrichia Khxdeni, var. scotica, nov. 

 (PL XII. fig. 10.) 



Proportions : — L. 12. H. 9. 



A closely allied form comes from the Middle-Silurian 

 (Llandovery) rocks near Girvan, Ayrshire. It is shorter, 

 being more nearly semicircular ; the middle lobe is rather 

 more definitely egg-shaped, and there is a thick raised mar- 

 ginal rim in all. A smooth suhvariety was described and 

 figured as B. Kloedeni by one of us in the ' Monograph of 

 the Silurian Fossils of the Girvan District,' by Nicholson 

 and Etheridge, Jun., 1880, p. 218, pi. xv. figs. 8-8 if ; and of 

 the present strongly granulate form (fig. 10) we have seen 

 four imperfect specimens (in Mrs. Gray's collection) from Bar- 

 gany-Pond Burn. Of these, one small hollow cast, preserving 

 the best proportion of characters, is here figured ; but the mid- 

 lobe is higher up than in older individuals. Excepting this 

 lobe the surface bears large scattered granules, sometimes 

 concentrically arranged, and the raised margin has a distinct 

 row of them also. The specimens occur in a hard limestone 

 and have not been got out free of matrix. 



3. Beyricliia concinna, sp. nov. 

 (PI. XIL figs. 22 a, h.) 



Proportions :— L. 10. H. 5. Th. 5. 



This little unique carapace is very neat, compact, and 

 semiovate, deeply impressed in the dorsal region of each valve 

 with two short and unequal sulci, marking off a short and 

 distinct midlobe. This is continuous with the general con- 



* See Nicliolson and Etheridge's ' Monograph Silur. Foss. Gu-van, 

 vol.i. 1880, p. 219 (references, kc). 



t We may here mention that a few other Beyrichice and Primitice from 

 Girvan remain to be described. 



