104 The Ottawa Naturalist [December 



distinctly flattened, the area facing diagonally upward- thus producing 

 a strongly angular outline a short distance above mid-height on the 

 right side of the the theca. The arrangement of the thecal plates on 

 this specimen is indicated by diagram No. 5. A part of the thecal 

 plates are missing- the specimen being imperfect, but all of the basal 

 plates are preserved, and, of these, seven appear to be in direct contact 

 with the top of the column. These are indicated in the diagram by the 

 heavy basal margin- 

 In most other respects, than those cited above, Comarocystites 

 shumardi closely resembles Comarocystites punctatus- The transverse 

 apical food-groove (Figures 1 A, B, C, and diagram No. 6) branches 

 at each end dichotomously, along the adoral side of the nodular 

 stereom protuberance which supports the right or left pair of arms. 

 Only the facets for the attachment of these arms are preserved, the 

 .arms themselves not being retained in any specimen at hand. 



The mouth or entrance into the theca consists of a small opening 

 located at mid-length along the transverse apical food-groove, at the 

 proximal end of the suture between plates a, a, in the diagram. The 

 food-groove is covered by a double series of covering-plates. Two 

 peristomial plates typically are in contact with the posterior margin of 

 the transverse apical food groove, and of these the right peristomial 

 plate is distinctly the larger (Diagram No. 5). From the center of the 

 latter, the linear hydropore ridge (Figure 1C on plate IV, also dia- 

 grams 5 and 6) extends diagonally downward and toward the right, 

 toward the center of the plate adjoining it on that side. One specimen 

 shows a minute pore immediately beyond the upper left hand end of 

 the hydropore ridge. There is no evidence of this being a constant 

 feature. 



The anal pyramid is not preserved in any specimen at hand- but 

 the circular opening into which this pyramid fitted (Figure IB on 

 plate IV) is preserved in several specimens, and this shows a diameter 

 of 3 millimeters in a specimen 25 millimeters in height. This circular 

 opening is surrounded by five thecal plates occupying the same position 

 as in Comarocystites punctatus. 



Text figure No. 6. Diagram of a few of the thecal plates at the apical 

 end of the specimen represented by figure 1C on plate IV: the number- 

 ing and lettering as in text figure No. 4. The transverse apical food 

 groove, branching at each end, -where the facets of the two pairs of 

 arms are located, the location of the mouth, the anus, and the linear 

 hydropore also are indicated. Special attention is called to the 

 monopolizing of the space posterior to the transverse food-groove by 

 the plate marked rp. In other specimens there is room, for smaller 

 plates on the left. 



