102 



The Ottawa Naturalist 



[December 



type specimen agree with the description of Comarocystites punctatus 

 given by Billings which lead Meek and Worthen to diagram 

 Comarocystites shumardi as having three basal plates. (Geol. Surv. 

 Illinois, 3, p. 292). At the time this diagram was prepared a part of 

 the plates of the type specimen of the latter species still were covered 

 by the matrix. Recently the writer removed this matrix and a new 

 diagram has been prepared (Text diagram, No. 4). 



Anal Side 



Text figure No. 4. Diagram of the thecal plates of the type specimen 

 of Comarocystites shumardi, replacing the diagram published by Meek 

 and Worthen in the report of the Geological Survey of Illinois, volume 

 III, page 292. In order to compare this diagram with that in the 

 Illinois report, the page should be turned so that the part marked anal 

 side forms the bottom of the figure. Additional plates have been ex- 

 posed recently by removing the matrix. The position of the nodular 

 stereom protuberance supporting the left pair of arms is indicated at 

 1, 2. The approximate location of the. anal pyramid is indicated by A. 

 The apical part of the theca surrounding the right pair of arms, as far 

 down as the plates bordering on the lower side of the anal opening, is 

 missing. The diagram is not intended to suggest any radiate structure 

 in the arrangement of the thecal plates. It is intended, however, to 

 suggest the presence of more than three plates in the basal series, 

 although the evidence in the particular specimen here diagrammed 

 is obscure. 



