253 



base subcircular or ovately-subcirciilar, the posterior end being usually 

 a little broader than the anterior, and sometimes nearly straight or 

 faintl}^ emarginate in the centre. Apex erect, obtuse in some specimens 

 and more acute in others, subcentral but always placed a little behind 

 the middle and sometimes as far back as half-way between the middle 

 of the valve and the postei-ior margin. 



Surface polished and shining to the naked eye, but when examined 

 with a somewhat powerful simple lens it is seen to be marked with 

 numerous minute and concentric laminar stj-ise, and there are traces 

 also of still more minute radiating lines. Test very thin. 



Muscular impressions very indistinctly defined : under a lens they 

 appear to consist of two somewhat reniform or arcuate scars, one on 

 each side of the apex, which seem to be divergent posteriorly and 

 convergent anteriorly, though they do not appear to meet in fi-ont. 



Length of the most perfect specimen figured, seven millimetres: 

 greatest breadth of the same, six mm. anda-half : approximate height, 

 three mm. 



South side of Maud Island : eight itpper valves, or casts of the upper 

 valve. 



As the number and shape of the muscular scars on the interior are 

 by no means clearly apparent, it is just possible that this shell may be a 

 Helcion, but its character, on the whole, are much more like those of 

 a Discina. 



GENEEAL CONCLUSIONS. 



1. The LTppER Shales and Sandstones, or Subdivision A. 



These rocks, which so far as known contain Inoceramus p?'oble'maticus 

 only, probablj^ represent the lowest division of the Upper Cretaceous. 



2. The Coarse Conglomerates, or Subdivision B. 



No fossils that can be identified specifically have yet been collected 

 from these deposits, but from their stratigraphical position they may 

 be presumed to be synchronous with the Upper Greensand, or Craie 

 Chlorite^ of the French Geologists, and with the Shales and Sandstones 

 of the " Dakota Group." 



