492 GASTEROPODA OF THE INFERIOR OOLITE. 



clathrata have already been partially indicated. Attention is also drawn, in 

 the accompanying footnote, to another form, lately found in the Lias of Thorn- 

 combe, which evidently belongs to the same group, though generically, or at least 

 subgenerically, distinct.^ 



Chilodonto'idea oolitica is a rare species, yet it occurs on the same horizon at 

 four localities, viz. the Goncaviis-bed at Bradford Abbas and the Irony Nodule-bed 

 of Burton Bradstock ; also at Beaminster and Stoford. 



455. FossAEus (CuuTHouYA^) ooLiTicus, sp. nov. Plate XLII, fig. 17. 



Description : 



Height . . . . .13 mm. 



Body- whorl to total height . . . 70 : 100. 



Spiral angle ..... 60°. 

 An ovate elongate shell with a short spire and few whorls, which are non- 

 embracing. A. very slight umbilical fissure. The entire shell is ornamented with 

 strong spiral ribs, regular and equidistant. Aperture a lengthened oval, with an 

 arched and crenulated outer lip, expanded anteriorly, and a long and almost 

 straight columellar lip. The entire peristome is thick. 



delations and Distribution. — There is very little difference between this shell 

 and the existing Couthouya reticulata, A. Adams, from the China seas. The 

 modern shell has a better developed umbilical fissure, and is rather smaller ; Isajns 

 fenestrata, Carpenter, from the west coast of North America, is also very near. 

 A single specimen from the Concavns-hed, Bradford Abbas. 



^ In order to find a place for the Lias shell, I propose to constitute the genus Wilsonia, thus 

 named in honour of Edwiird Wilson, Esq., F.G.S., Curator of the Bristol Museum, who is our chief 

 authority on the Gasteropoda of the Lias. The following is the diagnosis : 



Shell small, very thick, irregularly pupseform, imperforate, whorls increasing irregularly and scarcely 

 convex, separated Ly a distinct but rather narrow suture. Ornaments pronounced, consisting of four or 

 Jive granular spiral belts in each whorl, with fine intermediate axial decussation. Body-whorl rather 

 shorter than the spire and compressed. Aperture sub-circular, with a thick outer lip and two prominent 

 teeth towards the middle of the short columella. 



Wilsonia liassica, sp. nov. (Plate XLIV, figs. 13 c, 13 i, 13 c), has seven or eight whorls and a 

 total height of about 14> mm. The prominence of the penult, which quite equals the body-whorl in 

 width, is a characteristic feature ; the ornamentation is very rich. A single specimen from the 

 "junction-bed," Thorncombe, Dorset. 



In Wilsonia the aperture possesses two distinct teeth: in Chilodonto'idea there are three 

 callosities or teeth, and the internal portion of the aperture thus assumes a somewhat keyhole- 

 like shape : in Chilodonta the aperture is restricted by five irregular teeth, and thus becomes still 

 more fanciful in outline. We can scarcely doubt that these three genera (or sections) stand in 

 ancestral relationship to each other, either linear or collateral. 



2 Couthouya, A. Adams, 1860, sub-genus of Fossarus, Philippi, 1811, member of the Littorinidae. 

 Cf. also Fossariopsis, Laube, from the Trias. 



