196 PALEONTOLOGY OF OHIO. 



smallest difficulty, it is a matter of impossibility to determine, with the 

 materials at present in our hands, what are the true limits of the species. 

 Thus, specimens apparently belonging to C. pulchelltis may be picked out 

 which approximate to C. approximatus, Nich., and which thus tend 

 towards the type of C. Dalei, Edw. and H., since they possess tolerably 

 distinct surface tubercles. Others approach C. Fletcheri, Edw. and H., so 

 nearly, that it becomes absolutely out of the question to draw a rigid line 

 of demarkation between the two species, certain specimens being just as 

 properly referred to the one as to the other. In this way C. pulchellus is 

 brought into direct connection with C. gracilis, James, though typical 

 examples of the two species could not be confounded with one another 

 for a single instant. Again, the forms which I have here separated 

 under the name of C. sub- pulchellus form an unmistakable transition be- 

 tween C. pulchellus, in its proper form, and C. mammulatus, Edw. and H., 

 the latter belonging to the frondescent and laminated section of the 

 genus. In spite, however, of the close relationships thus indicated, it 

 seems in the meanwhile expedient to give separate titles to such forms 

 as admit of ready identification, leaving it for future determination 

 whether these forms are in reality entitled to rank as distinct species, or 

 whether they may be merely different phases of one very variable species. 

 Locality and position : Cincinnati group, Cincinnati, Oliio. 



ChyETEtes sub-pulchellus, Nicholson. 



Plate 21, figs. 6, 6a. 

 Corallum branched, the branches usually hollow, always more or less 

 compressed, and sometimes so much flattened as to become frondescent. 

 Greatest diameter of the branches, from four lines to nearly an inch. 

 The average corallites are circular or polygonal in form, with compara- 

 tively thin walls, about eight in the space of one line, with or without 

 a few very minute cylindrical tubuli interspersed amongst them. Interca- 

 lated amongst the ordinary corallites are rounded or sub stellate spaces, 

 about one line in diameter, and placed nearly one line apart, which are 

 occupied by tubes of two kinds. The exterior of each of these spaces is 

 formed by a ring of corallites which are slightly larger than the aver- 

 age, about six of them occupying one line. Inside this ring is a series 

 of from twenty to forty excessively small cylindrical tubuli, forming a 

 little 'bluster of pin-like punctures or perforations. The composite clus- 

 ters of large and small corallites thus constituted are very slightly or 

 not at all elevated above the general surface, and they melt away in^ 

 sensibly at their margins into the ordinary corallites. 



