Section TV, 1889. [ 75 ] Trans. Eoy. Soc. Canada. 



VT. — Descnjyfiniis of elglii New Specici of Fossils from flic Cam/n-o-Sihirian Rods of 

 Manitoha. By J. F. Whiteaves. [Phites XII to XVII.] 



(Re.ad May 8, revised Oct. 2(), 1889.) 



GASTEROPODA. 



Maclurea Manitobensis. (N. Sp.) 

 (Plate XII, aud Plate XIII, figs. 1 and 2.) 



Shell large, attaiuiug to a maximum diameter of eight incheis aud a half, aud cou- 

 sistiug of aboiat five .somewhat sleuder volutious which increase rather slowly iu size : 

 outer volïitiou nearly always distinctly angulated at the periphery. Left side almost 

 flat, but faintly depressed in the centre in some specimens and as faintly raised in others : 

 volutions, as viewed on the flat side, A^ery shallowly concave in the centre and slightly 

 raised on their outer margins : suture lightly impressed. Right side moderatelj^ convex 

 (the greatest thickness or depth varying in different examples from two fifths to one third 

 the maximum diameter) : somewhat conical or subhemispherical, the outer volution 

 obliquely flattened and narrowing A'ery rapidly, but in a few specimens somewhat 

 convexly, from the periphery to the umbilical margin: umbilicus deep, conical, and 

 apparently about equal in breadth to one fourth of the maximum diameter, though iu all 

 the specimens collected the test is either imperfect or absent at the umbilical margin : 

 aperture obliquely and rather narrowly subtrapeziform : outer lip apparently simple : 

 test thick. 



Surface of the test ou the left or flat side marked with irregularly disposed, Imt for 

 the most part distant, transverse linear grooves or periodic arrests of growth, each of 

 which curves gently backward in a very shallowly convex curve, and occasionally with 

 a few striations which run parallel to them. In one of the specimens figured (Plate XIII, 

 fig. 1) which is a little less than four inches in its greatest diameter, and in which the 

 whole of the test is preserved on the flat side, there are six of these periodic arrests of 

 growth on the outer volution, while the inner whorls are perfectly smooth. In larger but 

 similarly preserved specimens these arrests of growth, which are not sufficiently deep to 

 produce any impressions on the casts, are somewhat more numerous and disposed at still 

 more unequal interA^als. On the right or coua'cx side the test is ornamented with rounded 

 spiral ribs of nearly equal size, and these are crossed by similarly shaped, straight and 

 trausA^erse costa?, in such a way as to present a somewhat nodulous appearance. The 

 spiral ribs, howcA'^er, seem to be rather broader than the narrow furrows between them, 

 while the transverse costœ are apparently equal iu breadth to the regularly concave 

 grooA'es which alternate with them. 



