1916] The Ottawa Naturalist 79 



in different specimens. All efforts to diagram the basal thecal 

 plates of Comarocystites punctatus in such a manner as to secure 

 a primary series of 3, 4 or 5 plates has failed, nor is it possible 

 to demonstrate the presence of any radial plan of arrangement 

 of the lower thecal plates, extending outward from a supposed 

 primary basal series. 



If any increase in the number of plates forming the theca 

 takes place in any except the earliest stages of growth, this in- 

 crease in number can take place only at the base of the theca, 

 where in contact with the column. Elsewhere the plates of the 

 theca are almost uniform in size. The series of plates in con- 

 tact with the column, however, frequently are unequal in size, 

 smaller plates not infrequently being wedged in between larger 

 ones, and the line of contact between the margin of the lowest 

 plates and the top of the column is more or less irregular. 



EXPLANATION OF PLATE II. 



Fig. 1. Comarocystites punctatus Billings. Specimen belonging to James E. Narraway. 

 A, anterior side, photographed so as to show the thecal plates nearest the trans- 

 verse apical food-groove, and coverplates on the anterior side of the food-groove; 

 also the position of the anus and of the masses of stereom supporting the two 

 pairs of arms. Several of the plates give distinct indications of the pairs of 

 lunate pores which occur directly beneath the epistereom. B, posterior side, 

 photographed so as to show the thecal plates along the upper half of the specimen, 

 the cover plates on the posterior side of the food-groove, and the linear hydropore 

 passing from the right posterior plate diagonally backward and to the right 

 toward the middle of the adjoining plate. The facet for the support of the left 

 posterior arm and the branch of the food-groove leading to the margin of this 

 facet are well preserved; only a short part of the adjoining branch of the food- 

 groove is seen. The tipper part of the mass of stereom on the right of the food- 

 groove has broken off beneath the level of the facets supporting the right pairs 

 of arms. In both figures the anal pyramid is located on the right. C, five of the 

 cover-plates of the food-groove enlarged. D, one the thecal plates enlarged so 

 as to show the indications of th e presence of pairs of lunar pores presented by 

 the epistereom in unweathered specimens. A, B, enlarged 3 diameters; C, en- 

 larged 13 diameters; D, enlarged 8 diameters. The form and relative location of 

 the thecal plates of this specimen are indicated in text diagram 1. 



Fig. 2. Comarocystites punctatus Billings. Specimen belonging to Walter R. Billings; 

 view of right side, magnified 2.4 diameters. Photographed so as to show the 

 anal pyramid, the thecal plates immediately surrounding the anal pyramid, and 

 the diagonal arrangement of the thecal plates on this side of the specimen. 

 Indications of the transverse apical food-groove terminating at the two masses 

 of stereom supporting the pairs of arms are seen along the upper part of the figure. 



Figs. 3, 4. Comarocystites punctatus Billings. One of the brachials and one of the 

 pinnulars of the type illustrated on plate III, magnified. 3, three views of a 

 brachial, magnified 3 diameters; A, cross-section with indication of facet for 

 attachment for the pinnule on the right; B, side opposite the facet; C, side 

 showing the facet. 4, three views of a pinnular, magnified 6 diameters; A, cross- 

 section; B, side opposite the cover-plates; C, side showing three cover-plates 



along one edge. 



{To be continued) 





