1916] The Ottawa Naturalist 103 



The height of the type specimen equals 39 millimeters, the lateral 

 diameter is 34 millimeters, and the diameter from front to rear is 30 

 millimeters. The top of the column at its junction with the theca 

 was 6 millimeters in diameter. The left half of the apical transverse 

 food-groove, with its bifurcation on the proximal side of the stereom 

 mass supporting the left pair of arms is distinctly shown, but the right 

 half and all adjacent parts, including the anal area, are missing. Both 

 the apical area, as far as preserved, and the basal series of thecal 

 plates appear compressed in a vertical direction, and there is no reason, 

 judging from other specimens, for believing that the horizontal position 

 of these basal plates is a specific characteristic. 



Most of the specimens of Comarocystites shumardi so far seen 

 exceed 25 millimeters only slightly in length. In thecal plates 6 

 millimeters in width, the depth of the concavity may equal 1.7 milli- 

 meters. At the bottom of the concavity there frequently is found a 

 circular flattened or slightly convex area, about three-fourths of a 

 millimeter in diameter. 



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Text figure No. 5. Diagram of the thecal plates of the specimen 

 represented by figures 1A, IB, on plate IV. The plates on the right 

 side of the vertical sinuous dotted line on the right side of the diagram 

 duplicate some of the plates at the extreme left of the diagram. The 

 anterior peristomial plates are lettered a, a; the right and left posterior 

 peristomial plates are lettered rp and lp respectively. From plate rp 

 the linear hydropore extends diagonally downward and toward the 

 right toward the middle of the next plate. The relative position of the 

 four arms is indicated by the numbers 2, 1, 5, 4. The location of the 

 anus is indicated by the letter A. The basal plates in actual contact 

 with the top of the column, seven in number, are heavily margined at 

 the bottom. Several of the thecal plates on the left side of the speci- 

 men are missing. 



In the specimen in the Chicago University Museum, illustrated by 

 figures 1A and IB on plate IV, the area surrounding the anus is 



