88 * The Ottawa Naturalist. [November 



Grant. The first presents a clearly defined view of the lower half of 

 the right posterior arm, with its attached pinnules. The second pre- 

 sents a much less clearly defined view also of what appears to be the 

 right anterior arm, with its attached pinnules. Evidently both the 

 brachials and pinnulars of these two arms are arranged in uniserial 

 order. It is assumed that the left pair of arms presented the same 

 characteristics. Only the right posterior arm attached to the Billings 

 type-specimen is here described in detail. 



Twelve brachials (Brachials 1 to 11 are numbered in the figure 

 on plate III) are exposed, and each bears a single pinnule on its right 

 side. All of the brachials above the first are flattened slightly from 

 front to rear (Plate II, figs 3A, B, C), the ratio of the lateral diameter 

 to the adoral-aboral diameter being as 10 to 9 (Fig. 3A). The length 

 of each brachial usually equals about three-halves of its lateral 

 diameter. The facets supporting the pinnules are concave (Fig. 3C), 

 their margins being distinctly elevated, especially on their lower sides. 

 The location of these facets is slightly above the middle of each 

 brachial. On that side of the brachial which is opposite the pinnule 

 (Fig. 3B), the brachial tends to be slightly more angular in a direction 

 parallel to the length of the arm. The original length of the complete 

 arm is unknown, but probably it equalled about three-halves of the 

 length of the theca. The rate of tapering of the successive brachials, 

 as far as preserved, is but moderate. Analogy with Amygdalocystites 

 and Canadocystites suggests that the pinnules of all four arms of 

 Comarocystites were attached to the right side of the arms, the aboral 

 side of each arm facing the observer, and the distal end being directed 

 upward. 



16. The pinnules. The length of the pinnules probably 

 equalled 30 millimeters, and may have reached 35 millimeters. There 

 is but little variation in the length and width of the pinnulars, about 

 four occupying a length of five millimeters. Except in the case of the 

 first two or three pinnulars, most of the pinnulars are strongly flattened 

 transversely (Plate III; also figs. 4A, B, C, on plate II), the pinnules 

 being placed, for purposes of description, in an approximately vertical 

 position, with the aboral side facing the observer. The ratio of the 

 transverse diameter to the adoral-aboral diameter (Fig. 4A) is about 

 8 to 5. The lateral edge of the pinnulars (Fig. 4B) tends to be more 

 or less angular in a direction parallel to the length of the pinnule, 

 thus giving the pinnulars a lens-shaped cross-section. 



In the Billings type-specimen, here figured, a series of small, flat, 

 quadrangular plates lines one side of two joints of that fragment of the 

 pinnule which is marked Don plate III, and traces of similar small 

 plates are seen at the point C, on one side of the pinnule attached to 

 the eighth brachial. (See also fig. 4C on plate II.) These small 

 quadrangular plates are interpreted as covering-plates. Their number 



