1916] The Ottawa Naturalist. 89 



varies from three in a length of one pinnular, to five in a length of two 

 of these pinnulars. 



17. The absence of food-grooves on the brachials. In case of 

 the right posterior arm of Comarocystites, one of the branches of the 

 transverse apical food-grooves rises for a short distance along the 

 ventral side of the first brachial, but disappears before reaching the 

 top of this brachial. There are reasons for believing that the absence 

 of food-grooves on the arms of Comarocystites is secondary and not 

 primitive. The small quadrangular covering-plates along one side of 

 the pinnules, as described above, suggest the former presence of a food- 

 groove. As a matter of fact, no trace of an actual food-groove has 

 been noticed so far on any pinnular, but analogy with Amygdalocystites 

 demands that they should be present. 



In Amygdalocystites the food-groove follows one of the narrower 

 sides of the pinnule, the pinnulars being compressed laterally, and the 

 food-groove faces the mouth. In a similar manner the few covering 

 plates found so far on the pinnulars of Comarocystites are on the side 

 facing the mouth, and the sides of these pinnulars are even more 

 compressed than in Amygdalocystites. Originally, a food-groove must 

 have followed that side of the pinnule supporting the covering-plates, 

 and a second series of covering-plates must have existed along the 

 same side, but beyond the food-groove. Formerly the food-groove on 

 the pinnulars must have connected with one of the brachials, thus 

 reaching the transverse food-groove along the apical side of the theca, 

 if the analogy between Comarocystites and Amygdalocystites and 

 Canadocystis is as great as here suspected. It should be noted, how- 

 ever, that the facets supporting the pinnules of Amygdalocystites are 

 distinctly indented on the side where the branch from the food-groove 

 on the arm passed on the base of the attached pinnule. In Comarocy- 

 stites, however, the facets supporting the pinnules are circular, and 

 show no such indentation. Evidently the absence of a food-groove 

 extends to the lower pinnulars at least. 



18. The column or stem. The column or stem is cylindrical, 

 with no evidence of pentamerism either exteriorly or interiorly. The 

 segments or columnals are very thin, alternating in thickness, about 

 20 occurring in a length of six millimeters in the column attached to 

 that Billings type-specimen which retains the arm. This column has 

 a diameter of four millimeters. The surface of the column is orna- 

 mented by minute granules, seven in a width of one millimeter, 

 arranged quincuncially, in diagonally intersecting rows. The lumen 

 equals about one-fourth of the diameter of the column. The fiat 

 surfaces of the columnals are striated radially. The only known 

 complete column is attached to the specimen discovered and described 

 by Sir James Grant, and figured by him in the Transactions of the 

 Ottawa Field-Naturalists' Club, in 1880. In this specimen the 



