197 



"In 1890 Messrs. Dowling and Lambe collected an operculum, which is 

 probably that of a large specimen of this species, at Jack Fish Island, 

 opposite the mouth of Jack Fish River, Lake Winnipeg. "This opercu- 

 lum, which is represented in outline in the wood-cut, is a little more 

 than four inches in height or depth, and not quite three inches in its 

 maximum breadth. Its outer surface is coimpletely buried in the matrix, 

 the inner surface only being exposed. In the wood-cut the side indi- 

 cated by the letter A clearly corresponds to the outer side of the shell, 

 and the concave side opposite, — B, — to the inner or columellar side. The 

 side marked C corresponds to the flattened spiral side of the shell, and 

 that marked D to the inner wall of the umbilicus. The margins of 

 the sides C and B, whose junction forms the 'nuclear angle,' are thick- 

 ened, but the edges of the other two sides are very thin. This 

 thickening of the sides C and B is immediately followed by a shallow 

 depression in the nuclear region, but the inner side of the operculum 

 is otherwise nearly flat. The surface markings of this side consist of 

 numerous concentric raised lines of growth, but there are no clear indi- 

 cations of any "internal projections for the attachment of muscles.'' 

 Although the opercula of M. Logani, Salter, and M. crenulata, Billings, 

 are known to be provided with well developed" projections or "muscular 

 processes on the inner side, this is by no means always the case in other 

 species of the genus. On page 238 of the first volume of the "Palaeo- 

 zoic Fossils " of Canada, E. Billings distinctly states that there are no 

 muscular processes on the inner side of the operculum of his M. oceana, 

 and on page 243 of the same volume he figures opercula of two other 

 species of Maclurea, from Cape Norman, Newfoundland, in which there 

 are no muscular processes on that side.' ' In' the Museurri cif the Geological 

 Survey at Ottawa there are two opercula from the Calciferous of' the 

 Mingan Islands, which were referred by E. Billings, with some doubt, to 

 the M. matutina of Hall. There are no processes on the inner side of 

 these opercula." 



According to Messrs. Ulrich and Scofield (op. cit., p. 194), their genus 

 Maclurina (which the writer prefers to regard, for the present, as a 

 subgenus) is proposed for " the reception of shells heretofore classed as 

 Maclurea, but differing from the typical- form of the genus in wanting 

 the projections for the attachment of muscles on the inner side of the 

 operculum." '■'Maclurea Manitohensis, Whiteaves, the operculum of 

 which is figured and described by Whiteaves in the Canadian Record of 

 Science for April, 1893, is regarded as the type of the new genus." "In 

 this species the nucleus is at the junction of the lower and inner margin 

 of the operculum, and we believe the same is true of M. cuneata and 

 M. subrotunda of Whitfield, which, with WMteaves's species, are all that 

 at the present time it seems safe to refer to Maclurina." , 



