NATURAL HISTORY SOCIETY OP GLASGOW. 99 



but is distinguished by the lateral position of the radiating 

 ridges in the latter, and other minor characters. The relation 

 between the two forms may be nearer than at first appears, as it 

 is stated of C. subantiquus, that other ridges " appear to have 

 originally existed in front and behind." Mr. Kirkby has examined 

 these plates, and, in a recent letter* exclaims, " surely they must 

 be far-back ancestors of C. antiqmts." 



Locality and Horizon. — Law Quarry, as before. 



Collections. — J. Bennie, J. Armstrong, J. Smith, &c. 



Cltitonellm Bennicanu*, sp. nov. — (PI. II., figs. 11-13.) 



Sp. Char. — Depressed or flattened patelliform, rather obliquely 

 oval, inequilateral, narrower in front than behind, and often 

 irregular. Apex 'remote from the front, scarcely differentiated from 

 the remainder of- the plate ; a deep furrow extends from the apex 

 to the front margin. Front margin acutely rounded, more or less 

 produced in the median line ; posterior margin obliquely truncated, 

 or obliquely concave. Inserted portion of plate in the form of a 

 narrow marginal rim, including in it the produced portion of the 

 front margin. The surface is ornamented by a series of radiating 

 ridges extending all round the plate, but less plainly defined on 

 the anterior third ; the ridges are crenulated by the presence of 

 innumerable granules, whilst between the larger, smaller ones are 

 occasionally interpolated. 



Obs. — It is quite within the bounds of possibility, although, I 

 think, not probable, that these plates may have formed part of the 

 shell-covering of the same mollusc as those last described. Without 

 any desire merely to create a species, I have separated them on 

 account of the difference in the general shape of the two plates, the 

 presence of the anterior furrow in the present form, and the much 

 more numerous and more widely distributed crenulated ribs. 

 Should further researches prove the two forms of plates to be 

 identical, I would suggest the retention of the above specific name 

 in recognition of Mr. J. Bennie's careful researches and discoveries 

 in the strata from which the remains are derived. 



The furrow extending from the apex to the front would tend to 

 ally the present plate to that described by the Baron de Eyckholt 

 as Sulcochiton, but the form and ornamentation of the respective 

 plates is quite different. 



* Dated Nov. 6, 1880. 



