32 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 22, 



from Scalpa identical in size with the same species found in the 

 Marlstone of Gloucestershire. The beds at Scalpa have been sup- 

 posed to be Inferior Oolite ; but the presence of Pecten cequivalvis, 

 of large size, in them is against that opinion. The fewness of the 

 specimens collected at Scalpa, added to the bad state of preservation 

 of those found, make it a desideratum that these beds should be 

 worked with the view of clearing away the doubt. Looking at Mr. 

 Geikie's sections, and comparing them with the section which ac- 

 companies Sir Roderick Murchison's paper on the Oolitic Rocks of 

 Sutherland, Ross, and the Hebrides*, I am disposed to think that the 

 geologist would be rewarded by the discovery of both Marlstone, 

 Upper Lias, and Inferior Oolite in the Island of Scalpa. 



Pecten, nov. sp. 



This specimen is distinct from all the other Middle Lias Pectines ; 

 but, as it is only an imperfect mould, it is impossible to give a dia- 

 gnosis of the species. 



Plicatula spinosa, Sowerby. 



Plicatula spinosa, Sowerby, Mineral Conchology, t. 245. f. 1-4 ; 

 Goldfuss, Petrefacta Germanise, t. 107. f. 1. 



This species is a very common shell in the Middle Lias of England, 

 France, and Germany, and is found in the Pabba-shales. The spe- 

 cimens from Pabba measure -f^-ths of an inch in height. 



Gervillia Maccullochii, Wright, nov. sp. 



Shell large, oblong, equivalved ; moderately thick anteriorly, and 

 thin posteriorly ; umbos acute, extending to the extreme limit of 

 the anterior border ; hinge-margin straight, about 3 inches long ; 

 anterior auricle absent ; posterior long, wing-like, but imperfectly 

 preserved ; folds of growth irregular, and strongly marked on the 

 mould ; a prominent carina passes in an oblique direction, from the 

 middle of the left valve towards the posterior border ; inferior border 

 very convex, which gives an unusual height to the shell ; anterior 

 border oblique, but nearly straight. 



Dimensions. — Length 5^ inches ; height 2| inches ; thickness 

 1^ inch. 



This fine specimen, which is unfortunately broken, was collected 

 from the Pabba-shales (Middle Lias). A portion of the posterior 

 wing and of the convex lower border are absent, so that my mea- 

 surements are only approximately true. The diagnosis, however, 

 will enable palaeontologists to distinguish this Gervillia, which is the 

 largest species yet found in the Lias ; the height of the shell, the 

 flatness of the valves, the straightness of the anterior border, the 

 acuteness of the umbos, and the convexity of the inferior border di- 

 stinguish it from G. lata, Phil. The size of the shell, the straight- 

 ness of the hinge-margin, and the irregular marking of the lines of 

 growth distinguish it from G. Icevis, Buckm., which is found in the 



* Trans. Geol. Soc. 2nd series, vol. ii. p. 353. 



