1916] The Ottawa Naturalist. 91 



Agelacrinites chapmani occurs in one of the lower layers of lime- 

 stone, and the Comarocystites was found about five feet above this 

 level. The exposures in the quarry belong to the upper part of the 

 Cystid zone. It is evident that the types of Comarocystites punctatus 

 were found in the Cystid zone, since Billings stated in his original 

 description that the specimens occurred "generally along the water's 

 edge, from the Rideau Falls to the Chaudiere." The remarkable 

 specimen obtained by Sir James Grant from an excavation on St. 

 Patrick street, near Chapel street, in Ottawa, also may have come from 

 the Cystid zone, but there are no exposures at present in this area, by 

 means of which the horizon may be established definitely. Evidently 

 Comarocystites has a considerable vertical range in the Trenton of the 

 Ottawa area, being unknown so far only from the Dalmanella zone, 

 at the base of the Trenton, and from the Hormotoma or Sponge zone, 

 at the top of the Trenton. In the intermediate zones it evidently occurs 

 at more or less remote intervals, and is a comparatively rare fossil. 



Possibly there are two species of Comarocystites in the Ottawa 

 area; one of larger size, with more compressed theca, and with nearly 

 smooth thecal plates; the other smaller, less compressed, with minutely 

 granular thecal plates, marked by pairs of distinctly lunate short 

 ridges. The second form is known to occur at the top of the Tetradium 

 zone, immediately beneath the Prasopora zone, and in the Cystid zone. 

 Possibly the smooth form occurs at a different horizon, but the num- 

 ber of well preserved specimens at hand is not sufficient to determine 

 whether the smooth and ornamented forms in reality are distinct or not. 



Comarocystites punctatus is cited by Rominger also from the 

 Trenton, in section 17 of township 41, above the big bend in the 

 Escanaba River, north of Little Bay de Noquette, in Michigan. 



20. Literature on Comarocystites punctatus: 

 Comarocystites punctatus Billings: 



Billings, Canadian Journal, 2, 1854, p. 270, figs. 1-3. 



Figure 1 in this paper corresponds to figure 2 on 

 plate V of Decade III. Figure 2 is an apical 

 view of the same specimen and corresponds to 

 figure 2b in the Decade, but is not identical with 

 the latter; there is no indication of a pair of arms 

 at the upper end of the figure, but only of a single 

 protuberance, and the location of the anal pyra- 

 mid beneath the pair of arms in the lower part of 

 the figure is shown. Figure 3 corresponds to 

 figure 1 of the Decade. 



Geol. Surv. Canada Rep. Progr. for 1853-56, 1857, 

 p. 288. 



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