4 CONTRIBUTIONS TO CANADIAN PAL.EONTOLOGT. 



to. Ill the district embraced by Ihe northern part of tlie map it has 

 been found difficult to cany out a similar lithological subdivision of the 

 formation, and no attempt has lieen made to indicate such subdivisions 

 on the map. Still further northward, in Ihe district from which the 

 greater number of the fiissils collected by 3Ir. J. B. Tyrrell were 

 obtained, it becomes quite impossible to distinguish the three subdi- 

 visions above refei-red to. The mollusca from this district, however, 

 are f >r the most part from the lower portion of the Laramie, and con- 

 sequentlj' from a horizon nearly or quite equivalent to that occupied 

 in the typjical region by the St. Mary Piiver Series. In the jn-esent 

 paper, under the heading A. of the '■ TVcstern Laramie ' and in section 

 3, the sjiei-ies collected from the St. Mary Eiver Scries proper will be 

 sepai'ately designated as such. The remainder are from the lnwer por- 

 tion of the Laramie in its noithern extension, with the exception of 

 six species from the same northern region, which occupy positions so 

 far u]) in the Laramie that the beds in which they occur may possibly 

 represent the Willow Creek or Porcupine Hill Seiies. These again 

 will be specially designated, though they are included in the present 

 section for convenience of de-cription. With the exception of these 

 last-mentioned species, the mollusca here described or enumerated in 

 section .3 of subdivision A may be considered as representing the fauna 

 of the lower part of the Laramie of the region. 



LAMELLIBEANCHIATA. 



AnomIA PERSTEHiOSA. (X. Sp.) 



Plate 1, fig. 2. 



Upper valve (assuming that tlie shell is an Anomia) moderately con- 

 vex, irregular in outline, and varying from subcircular to obliquely 

 fiubovate, sometimes slightly arcuate and curved to the left. Beaks 

 marginal, small, but in some si)ccimen9 rather prominent. 



Surface marked by radiating raised lines, a few of which, at distant 

 but irregular intervals, are conspicuously broader and more prominent 

 than the rest. Under an ordinary simple lens, these radiating lines 

 are seen to be subnodulous, in consequence of their passing over the 

 fiiint concentric lines of growth. Under valve and characrers of the 

 interior of the upper unknown. 



Upper Belly Eiver, twentj-three miles ab.ive the mouth of the Water- 

 ton, E. G. McConnell, 1881 ; Si. Mary Eivcr Series: three specimens. 



