126 TT. H. Hiidkston—The YorksJiire Oolite. 



Shell oval, depressed ; apex (imperfectly preserved) near tlie 

 anterior margin. Ornamented w^ith longitudinal radiating ribs, 

 •which are fine and wavy, and partly deflected where they are 

 decussated by a few encircling rugose bands. The condition of tlie 

 specimen scarcely admits of closer description. 



Belations and Distribution. — From the bulk of the Minchinhampton 

 specimens this variety is clearly distinguished by the fine and more 

 wavy character of the longitudinal radiating ribs. Still these are 

 not so fine as those shown in Buvignier's figure of P. Mosen^is. 



No instance of any variety of Patella rugosa having been found 

 on this horizon in other parts of England is known to me, so that 

 this specimen from the hard Eag of North Griraston is almost 

 unique. An imperfect specimen from the Upper Calcareous Grit of 

 Pickering may belong here. 



Order Opisthobranchiata, M. Edwards. 



This section of the Gasteropoda is so poorly represented, and the 

 specimens are for the most part in such bad preservation, that very 

 little can be said on the subject, which must be disposed of briefly. 

 Genus Bulla, Klein, 1753. 



Shell oval, ventricose, convoluted. Apex perforated. Aperture 

 longer than the shell, rounded at each end, lip sharp. 



55. — Bulla (? Akera) Beaugrandi, De Loriol, 1874. 

 Plate IV. Eig. 6. 



Akera BeaugruncU, Loriol, 1874, Loriol and Pellat, Et. Sup. Jurass. de Boulogne, 

 vol. i. p. 38, pi. vi. fig. 1. 



Description. — Specimen from the Coral Eag of Ayton (my 

 Collection). 



Length, restored 40 millimetres. 



Width across centre 24 , , 



Shell oval, moderately elongate, contracted at either extremity, 

 and slightly tumid in the middle. Spire apparently composed of 

 two or three w^horls. The last is very large, and has its surface 

 covered with broad and very marked lines of increase, w^hich, from 

 their prominence and irregularity, produce a certain amount of 

 sculpture on the otherwise smooth surface. The inner lip is broken 

 away anteriorly, and the outer lip so involved in matrix that a closer 

 description is impracticable. 



Belations and Distribution. — There is so little to distinguish the 

 various species of Bulla from one another that, when, as in this case, 

 a specimen is unique and deeply involved in matrix, some difiiculty 

 arises as to its correct identification. Altera Beaugrandi occurs in the 

 Pterocerian of the Boulonnais. In outline and proportions, and 

 especially in the broad lines of growth, the Ayton specimen greatly 

 resembles De Loriol's species. Unfortunately, there is no evidence 

 that the anterior portion of the columella is as much excavated as in 

 the type specimen. Buvignier has two species of Bulla, viz. B. 

 Dyonisea, Buv. (Stat. geol. de la Meuse, p. 28, pi. 21, figs. 25 and 26), 

 and Bulla Moreana, Buv. (op. cit. p. 28, pi. 21, figs. 33 and 34) — 

 both from the "argile de Kimmeridge" of the Meuse — which also 



