1916] The Ottawa Naturalist 7 7 



has figured a possible madreporite at the posterior end of the 

 suture between the two posterior peristomial plates making 

 it possible to orient this species in the same manner as Coma- 

 rocystites with the anal pyramid on the right side of the theca. 



9. The covering-plates of ike transverse apical food-groove. 

 The transverse apical food-groove is covered by two series of 

 quadrangular covering-plates (Plate II, figs. 1A, IB, also C), 

 one on each side of the food-groove. These plates meet along 

 the middle line of the food-groove so as to form an acute ridge. 

 They are ornamented by minute granules similar to those of 

 the adjacent thecal plates and there also is a tendency toward 

 a low elevation along the median line of each covering plate. 

 About five covering-plates occupy a length of 3 millimeters 

 along the food-groove. In one specimen 8 or 9 covering-plates 

 occupy the entire distance along the unbranched part of the 

 food-groove, and 3 or 4 covering-plates line each side of that 

 short branch of the food-groove which leads from the left end 

 of the food-groove to the base of the left posterior arm. In 

 another specimen about 15 or 16 covering-plates occur on each 

 side of the unbranched part of the transverse apical food-groove, 

 and 3 or 4 covering-plates line each side of the branches leading 

 from the left end of the food-groove to the bases of the left 

 anterior and left posterior arms. 



10. The anal pyramid. The number of plates exposed in 

 the anal pyramid (Plate II, fig. 2; also A in the text diagrams) 

 varies in different specimens from 5 to 6. The general form 

 of the pyramid is semi-globose, but the apical part is more or 

 less flattened. In all of the specimens examined, the anal 

 pyramid is bordered by 5 thecal plates. Of these, tw T o plates 

 form the lower border, one plate occtirs on each side, and the 

 fifth plate forms the upper part of the border. The plate on 

 the right side of the pyramid always is larger than the rest. 

 The upper margin of the plate forming the upper border of the 

 anal pyramid is overlapped on each side by a narrow plate 

 separating the latter from direct contact with the base of the 

 nodular stereom protuberance supporting the right pair of arms. 

 The sutures of these overlapping plates often are indistinctly 

 defined. That part of the thecal plates which borders directly 

 on the anal pyramid is smooth, and moderately elevated. 



11. Fixity in arrangement of thecal plates limited to the im- 

 mediate vicinity of the transverse apical food-groove and of the 

 anal pyra nid. Evidently there is a considerable degree of fixit 

 in the number of thecal plates bordering on the transverse apical 

 food-groove and in the number of those surrounding the anal 

 pyramid, and there also is an approximation toward fixity in 

 the general outline of these plates; but this fixity in number, 



