I 



Pahvozoic Corah of the State of Ohio. 93 



by faint but quite regular cruciform lines, as in C. rhomhicits 

 and several other forms. In sections taken parallel with 

 and close to the surface, the " monticules " are seen as so 

 many stellate spaces, occupied l)y an irregular network of 

 more or less angular and elongated cells, apparently repre- 

 senting sections of tubes obliquely proceedmg towards the 

 surface. The corallites appear as oval or circular tubes, 

 which fill up the spaces not occupied by the monticules, and 

 which are either hi contact or, more commonly, are sepa- 

 rated by a similar but closer angular network. No traces of 

 minute, interstitial tubuli can be detected in sections of this 

 kind. 



Dehayia attrita^ Nicholson. 



Cheetetes attrittts, Nich. op. cit. p. 194, pi. 21. fig. 4. 



This form properly belongs to the genus DekoT/i'a, and may 

 erhaps be nothing more than a slender variety of I), aspera, 

 Si H. I originally was inclined to believe that the genus 

 Dekayia was wholly inseparable from Cheetetes ; but thin 

 sections sliow characters which possibly may suffice for generic 

 separation, though there is in most respects the closest relation- 

 ship between the two groups. The little columnar eminences 

 which stud the surface oi Dehayia, and which alone distinguish 

 the genus from Chwtetes, are not, as I imagined, simply of the 

 nature of " monticules," but they are just as conspicuous in 

 sections as they are superficially. In cross sections (PI. V. 

 fig. 12) the ordinary corallites are seen to be more or less 

 polygonal, with thin walls, and destitute of interstitial tubuli. 

 The larger corallites are arranged in radiating groups, of five 

 or six each, the centre of each group being formed by one of 

 the surface-columns. As seen in sections of this kind, the 

 columns are somewhat polygonal, and are seen to be distinctly 

 hollow. As seen in long sections (PI. V. fig. 12 a), the 

 corallites in the centre of the colony are vertical, with thin 

 undulating walls, and destitute of tabulae. As they approach 

 the sui'face the corallites curve outwards, and a few remote 

 taVmlie are developed in them. No interstitial tubuli are present. 

 At intervals the walls of the corallites exhibit fusifonn thick- 

 enings, which become more abundant as the surface is ap- 

 proached, and which represent the surface-columns cut in long 

 section. As seen in sections of this kind, the columns are 

 also clearly hollow ; but their true nature is quite uncertain, 

 and it is doubtful if, of themselves, they are sufficient to sepa- 

 rate the genus from Cheetetes proper. 



