1916] The Ottawa Naturalist 75 



by the gut to reduce the convexity of the upper part of the 

 theca along its outline on the right, thus lowering the point of 

 maximum convexity on this side. 



6. The numbering of the rays of the food-groove system. 

 There is no trace of an anterior ray of the food-groove system 

 in Comarocystites. However, it is possible to number the arms 

 present in such a manner as to make comparisons with the 

 rays of cystids whose food-groove system shows evidence of 

 pentameral symmetry readily possible. (Plate II; figs. 1A, IB; 

 also text diagrams 1 and 2). 



f oo 4-".P.r. 0v e 



3 q00 p U oMPOn/ 



% 00 9 O o D Oo D *Vo 



Text figure No. 2. Diagram of the thecal plates of the specimen represented by 

 figure 2 on plate II. All letters and numbers as in text figure No. 1. That edge 

 of the thecal plates which is in contact with the anal pyramid is heavily blackened. 

 That edge of the basal plates which is in contact with the column is blackened 

 in a similar manner. 



In that case the left posterior arm is numbered 1, the left 

 anterior arm, 2 ; the right anterior arm, 4 ; and the right posterior 

 arm, 5. The absence of an anterior ray is indicated by the 

 omission of the number 3. 



7. The thecal plates bordering on the transverse apical food- 

 groove .- If the thecal plates bordering on the transverse apical 

 food-groove be termed peristomial plates, then the anterior 

 side of this food-groove (Plate II, fig. 1A) may be described as 

 bordered by two peristomial plates sufficiently similar in 

 width to place the intermediate suture-line about half-way 



