86 The Ottawa Naturalist. [Nov. 



one granule at each intersection of the lines. The lines of 

 growth, with a gentle curve towards the posterior margin, pass 

 from apex to apex across the longest diameter of the inesh. 

 Some of this very fine network is worn, and in places the granules 

 appear to be shoved up together, but there is much of it that is 

 remarkably well preserved. 



The length of the right valve, which is the only specimen 

 found, is 53 mm., height 21 mm. 



This species closely resembles Rhytim^'a oehana Ulrich, but 

 differs from it in the straight anterior cardinal margin in the 

 narrower and less oblique sinus, with its consequent less sinuate 

 ventral margin, in its narrow and more rounded posterior por- 

 tion. 



It differs from Rhytimya compressa Ulrich, in the more 

 abrupt downward slope of the anterior portion of the dorsal 

 margin, in the somewhat more distinct mesial sinus, and the 

 corresponding slight upward flexure of the ventral margin. 

 Rhytimya granulosa is larger, the posterior portion is more pro- 

 longed, and the mesial sinus is less oblique. 



Compared with Rhytimya convexa Ulrich, this species is less 

 convex on the whole, although slightly more inflated anterior to 

 the mesial sinus. The folds of concentric growth lines are less 

 prominent posteriorly and the cardinal margin is straighter. 



For this species I would propose the name Rhytimya 

 granulosa. 



The Museum is indebted to Mr. G. S. Blake, geologist of 

 the Standard Oil Company of Canada, for the shell. 



Formation : Lorraine, in the Proetus zone, several hundred 

 feet below the Sirophomena ftuciuosa horizon, which is regarded 

 as near the base of the Waynesville division of the Richmond, 

 by Aug. F. Foerste. 



Locality: Twelve miles east of Ottawa, near Vars, on the 

 Grand Trunk railroad. Immediately west of the intersection of 

 the roads between concessions VII and VIII, between lots 20 

 and 2 1 , nearly two miles west of Vars. 



Explanation of Plate II. 



RHYTIMYA GRANULOSA, N. SP. 



1. Portion of network on the upper posterior portion of 

 Rhytimya granulosa x ten diameters. The lines of nodes 

 from right to left are the radiating lines shown on the 

 specimen. The single long lines through the long axis of 

 the mesh are the lines of growth. 



2. Rhytimya granulosa, photograph of type x 1>2. Number 



4.319 in the Geological Survey Museum. 



