257 



oldest known of those allies of Cythere which have been divided 

 off as Cythereis- on account of their quadrate angular features. 

 The smooth test bears, in addition to the characteristic posterior 

 angles, the central tubercle usual in this genus, also a curved 

 lumpy ridge along the ventral region, and a smaller interrupted 

 ridge in the antero-dorsal region. 



Two specimens from the Blue FuUers-eai'th Clay, Midford. 



17, CYTHEREIS WALFORBIANA., sp. 11. 



PI. v., figs. V2 a, h, c. 



This is near to C. fullonica (pi. iv., fig. 13), but the surface is 

 somewhat differently sculptured. The anterior ridge is stronger 

 and more continuous, and ends sharply over the hinge ; the 

 dorsal ridge is not quite so acute posteriorly; the A^entral ridge 

 is somewhat weaker ; and there are two small longitudinal ridges 

 on the posterior third of the valve. These last are slightly curved, 

 and one of them bears a small smooth tubercle. 



One specimen from the base of the Fullers-earth Oolite between 

 Notgrove and Bourton. Collected by Mr. E. A. Walford, F.G.S., 

 after whom the species is named. 



18. CYTHERIDEA ^QUABILIS, Sp. «. 



PI. i., figs. 1 a, b, c. 



Oblong, with symmetrically rounded and equally compressed 

 ends ; the latter feature giving a truly lanceolate edge-view, longer 

 than broad, and diminishing each way from the middle. The hinge- 

 line (seen to the left in figure 1 a) is straight, with feeble angles, 

 thus associating this form with similar Cytheridecc (figs. 3 and 4), 

 which have this character definitely though weakly marked. 



Surface smooth, very convex, especially in the ventral region ; 

 end view, broadly ovate. 



At first sight this species is something like Cythere (?) tenella, 

 (Quart. Journ. Geol. Soc, vol. xl., 1884, pi. xxxiv., fig. 24) ; but 

 the present specimen is much larger and more symmetrical. 



