410 Prof. T. 11. Jones on tJie 



postero- ventral region. In the closed valves the ventral aspect 

 presents a bluntly tapering- anterior extremity and a truncate 

 hinder end, which is modified by the triangular union of the 

 rido-es continued downwards and forwards from the face of 



o 



the valve. 



Instead of the superficial ridge passing round the periphery 

 of the valve, as in the other species alluded to above, it seems 

 here to extend with an imperfect curve only towards the 

 centre and then to die out in a single median extension. 



Named after its discoverer, Mr. John Smith, of Kilwinning, 

 Ayrshire. 



One specimen : — Smith Coll. no. 57. Railway-cutting, 

 side of Severn, Ironbridge. 



VI. Xestoleberis, G. 0. Sars, 1865. 



1. Xestoleberis corbuloides (J. & H.). 



Cythcre corhuhides, Jones & Holl, Anu. & Mag. Nat. Hist. sor. 4, 

 "vol. iii. (1809), p. 211, pi. xv. figs. 4 rt-5 h. 



The sizes vary with age and in individuals ; in a full- 

 grown specimen the proportions are as follows : — 



Proportions:— L. 21. H. 13. Th. 15^. 



This seems to be referable to Xestoleberis because it much 

 resembles some members of that genus in certain features and 

 in general habit. See also Ann. & Mag. Nat. Hist. October 

 1886, p. 264, for a note on the Carboniferous X. ? subcor- 

 buloides, J. & K. 



( Vine Coll. no. x. Bed no. 46. Shales over 



Six V Wenlock Limestone, 



specimens : j xi. Bed no. 43. Coalbrook 



I Dale Beds. 



Mr. Vine has also met with this species in Beds no. 25 and 

 25*. Tickwood Beds. 



Eighteen f Smith Coll. no. 44. Sedgeley. 

 specimens : i ^^' I^'-vilway-cuttnig, side of 



^ V bevern, Ironbridge. 



VII. ^CHMINA, J. & H., 1869. 



^chmina, Jones & IIoU, 1869, Ann. & Mag. Nat. Hist. ser. 4, vol. iii. 

 p. 217. 



Hare specimens only of two species of this genus were 

 known in 1869 from the Wenlock Limestone near West Mai- 



