Palaozoic Corah of the State of Ohio. 89 



which nii<rht readily be taken for young forms of C. pctropo- 

 lita/ius. The characters shown by sections would appear, how- 

 ever, to render this liypothesis untenable, or, at any rate, un- 

 likely. As seen in transverse sections (PI. V. fi;,'. 7), the 

 coraiiites are irre^nilarly poly.t^onal or rounded, with thick 

 walls, and haviiijL^ numerous small tubes scattered amongst 

 those of the ordinary size. In vertical sections (PI. V. fig 7 a), 

 the coraiiites are seen to be directed upwards from the basal 

 concave epitheca, with a slight oblique curvature. Their walls, 

 at first thin, become thickened in aj)proaching the surface ; and 

 their interior is crossed by delicate and comparatively remote 

 tabuhe. Small tubuli are occasionally interspersed amongst 

 those of the usual dimensions; and these are more closely 

 tabulate than is the case with the full-sized coraiiites. It will 

 thus be seen that, both in horizontal and vertical section, 

 C. discoideus differs greatly from adult examples of C. petro- 

 politanus. 



Chcetetes Newherryi^ Nicholson, op. cit. p. 212, pi. 22. 

 figs. 4, 4 a. 



In external form this species is superficially very like 

 C. discoideus, James ; but its more minute external characters 

 are very different, and these differences are fully borne out 

 by an examination of the internal structure of both foi^ms. 

 The coraiiites appear, in transverse sections (PI. V. fig. 8), 

 as approximately circular tubes of nearly equal size, and 

 arranged in regular rows, those of contiguous rows being 

 sometimes placed opposite each other, sometimes alternately. 

 The walls of the coraiiites are thick ; and at every point 

 where four coraiiites come together is placed a small cir- 

 cular tube. Every corallite, therefore, is surrounded hy four 

 of these smaller tubuli. In vertical section (PI. V. fig. 8 a), the 

 coraiiites are directed upwards with a slight curvature from 

 the attached base, each being furnished with a few regular 

 and remote tabula}. Interspersed with the ordinary coraiiites 

 are minute tubuli, with numerous close-set tabular. In this 

 latter feature, this species, as is the case with several other 

 species of Chatetes [Monticulipora), reminds one forcibly of 

 the Heliolitidae. 



Chateics Jamesi, Nicholson, op. cit. p. 200, pi. 21. 



figs. ll,llrt. 



The internal structure of this fine species is very charac- 

 teristic. In the centre of the corallum, as seen in vertical 



