598 TRANS. ST. LOUIS ACAD. SCIENCE. 



around which the different laminae have grown, and extend 

 through the whole reef to bej'ond its surface. This last is a most 

 striking feature. The nucleus, referred to, has a diameter of more 

 than 1.5 centimetres, but the fracture shows the vermiform struc- 

 ture to extend into its substance as well as the smallest pores. 

 On the lower side of the fractured laminae, the smaller tubes 

 appear to be filled by hemispherical tabulse. The vertical section 

 shows about two laminae and two interlaniinar spaces in a milli- 

 metre thickness. A considerable portion of the typical reef was 

 probably obtained, and has a diameter of about eight centimetres. 



Besides the above description, it may be remarked that the 

 horizontal canaliculi are scarcely apparent. The specimen is 

 much silicified, and weathered so as to make visible the laminjE, 

 pores, and tubes. In places, however, where the organism is not 

 weathered, the supplemental filling of the spaces obscures the 

 laminae themselves. 



The general appearance closely resembles C. ivalkeri^ but it 

 can be distinguished by the peculiar large vermiform tubes origi- 

 nating from its own nucleus, and by not being a parasite. Only 

 one specimen has been obtained from the Niagara formation at 

 Hamilton, so far as I am aware. 



Genus CCENOSTOMA (Winchell, 1867). 



The real distinctive character of this genus, as stated in Dr. 

 Dawson's memoir on " Structure of Stromatoporidae" CQ. G. S., 

 1879), is the "absence of central simple radiating tubes, which in 

 these species are represented by a group of more or less diver- 

 gent ascending tubuli, so that the surface of the last layer presents 

 eminences not with a single large pore at summit, but with sev- 

 eral small pores diverging from their sides." 



CcENOSTOMA CONSTELLATUM (Hall). 

 Plate 6. Fig. 11. 



''Massive, hemispheric, spheroidal, or irregular; composed of 

 thin concentric layers which are penetrated by minute vertical 

 tubes or cells ; surface of layers nodulose, each elevation being 

 marked by an irregular stellate impression with undulating and 

 bifurcating rays; intermediate spaces smooth, or only having 

 minute cell-apertures." 



