128 Cincinnati Society of Natural History. 



liporce seem to be undoubtedly devoid of mural pores, but I have 

 examined .... a specimen from the Wenlock Limestone 

 of Dudley .... which has all the e.xternal and general 

 characters of such a Monticulipora as M. petropolitana, but in which 

 the walls of the corallites are unquestionably minutely porous." 



Third. — It is noticed that there is a difference between the 

 young and the old parts of the corallum, which may be called res- 

 pectively the immature and the mature portions. ''■ The walls 

 commence thin and apparently indivisible. This portion in the 

 ramose and frondescent forms occupies the deeper regions, and 

 terminates at or very near the point at which the tubes bend ab- 

 ruptly to the surface. Here the diaphragms are often wanting, and 

 are always more remote than in the mature region. Cystoid dia- 

 phragms and spiniform tubuli, (the spiniform corallites of Nichol- 

 son,) are never developed, nor are true interstitial tubes, these 

 appearing only in the mature region. The peripheral portion in 

 the great majority of forms, differs more or less from the immature 

 region. The tubes bend outward, the walls become more or less 

 thickened, and if at all, the cystoid diaphrams, interstitial tubes, 

 spiniform corallites and mural pores are developed. The dia- 

 phragms become more numerous and appear to be of a different 

 character. 



The thickening of the walls of the tubes is one conspicuous 

 feature of the mature portion, accompanied either by the addition 

 of concentric, or obliquely arranged and overlapping layers. This 

 addition of matter may take place continuously and regularly, or 

 periodically. It is not so easy to detect the two regions in the 

 massive as in the ramose and frondescent forms, since in some of 

 the massive ones the walls of the tubes remain thin, the diaphragms 

 are remote, and neither interstitial cells, nor spiniform corallites are 

 developed. In specimens of M. Jiliasa, for example, there are^ 

 sometimes many successive immature and mature zones, the first 

 marked by thin walls and remote diaphragms, and the other by 

 slightly thickened walls and crowded diaphrams. 



From this we gather that there are two layers in each corallum; 

 one, the immature, characterized by thin, indivisible tube walls and 

 few diaphragms; while the other, the mature, has the walls often 

 thickened, and cystoid diaphragms, spiniform corallites and inter- 

 stitial cells developed. Sometimes opercula, with a central open- 



*The following is condensed from Mr. Ulrich's account, in Jour. C. S. N. H., v. 



