Upper Palceozoic Shells from Madagascar. 9 



near the aperture to the width of the remainder of the 

 spiral system. 



Dimensions : 5 '5 by 4 mm. 



This fossil bears a remarkable resemblance to Miiller's 

 modern species Planorbis earinatus, which forms the type of 

 Stein's genus Tropidiscus , on account of the possession of a 

 peripheral carination. From its condition as a limonite 

 cast sculpture-markings are scarcely decipherable. It occurs 

 embedded on the inner surface of one of the nodules 

 accompanied by a fish-fragment, which, according to Dr. A. 

 S. Woodward, is not capable of determination. A basal 

 disc view of the specimen is exhibited on one half of the 

 nodule, whilst its counterpart in the other half shows a 

 discoidal interior of the outer volution as well as obscure 

 traces of the internal volutions. The specific name is applied 

 in honour of the discoverer. 



Pelecypoda. 



Naiadites madagascariensis , sp. n. (PI. I. figs. 8-11.) 



Shell small, subquadrate, oblique, submedianly elevated, 

 sloping laterally ; hinge-line straight ; umbones anterior ; 

 pallial line entire ; sculpture consisting of rather distant 

 concentric lines of growth and finer striations on the lateral 

 regions. 



Dimensions : 3'5 by 3 mm. 



The valves of this shell are grouped together on the 

 inner surface of one of the small nodules and appear 

 mostly as internal cavities, although a wax impression 

 reproduces satisfactorily their original external condition. 

 From this it is apparent that the shell with such characters 

 as are referred to may be identified with Dawson's genus 

 Naiadites, a freshwater form originally described from the 

 Coal-measure deposits of Nova Scotia, and founded on 

 the type of Naiadites carbonarius of the same author 

 ('Acadian Geology,' supplement to 1st edition, 1860, 

 p. 43, & 2nd edition, 1868, p. 204). Some of the interiors 

 show very clearly the simple and non-sinuate character of 

 the pallial impression ; but the details of the hinge are 

 quite obscure, from the result probably of immature growth, 

 so that no horizontal striations are observable, such as 

 Dr. Wheelton Hind regards as characteristic of this genus 

 (' Monograph Palseontographical Society/ 1895, p. 126). 



It is possible that the affinities of this mollusc may be 

 looked for between Dawson's N. carbonarius and N. modio- 

 laris of J. de C. Sowerbv, both of which occur in the coal- 

 formation of Britain and the Continent. 



