J 26 



Cincinnati Society of Natural History. 



numerous, and in some forms at least, appear to be of a different 

 nature from those crossing the tubes in the " immature" region. Take 

 for instanee any speeies of Callopora, such as C. elegantula, Hall, or 

 C. ramosa, D'Orb. (Monticulipora ramosa, D'Orb. ) At the ends of 

 the branches where the " immature" portion of the tubes is exposetf, 

 the cells are always found to be open, while over the sides of the 

 branch the cell-mouths are commonly closed b}' opercula, with a 

 central opening. In tangential and longitudinal sections, the tubes in 

 the u mature" region of the branch sometimes show a diaphragm 

 which is in all respects identical with the opercula closing the cell-aper- 

 tures at the surface of the zoarium, excepting that the central opening 

 has been filled with a secondary deposit of either a lighter or darker 

 colored sclerenchyma than the surrounding matter. It is due to the 

 last fact that we are enabled to know that these diaphragms have ever 

 been perforated, and I believe that we ma} T now safely assert, that the 

 diaphragms of the "mature" portion of the tubes (in at least the 

 species of Callopora and Stenopora), formed successively the opercula 

 of the preceding layer of cells. In Dekayia, at the final period of 

 growth of the outer layer of cells, a thin pellicle is drawn over the 

 orifices of the cells, which becomes the floor to the next succeeding 

 layer, and eventually a diaphragm in the tubes thus formed by the su- 

 perposition of numerous la} T ers of cells. The thickening of the walls of 

 the tubes is one of the most conspicuous features of the "mature" 

 region. It is accomplished either by an addition of concentric 

 laminae, as for example in the group of species t} T pified by M. pulchella, 

 E. and H. (Monotrypella, nov. gen.); or by a succession of obliquely 

 arranged and overlapping laminae. In the latter cases the addition of 

 this calcareous matter may take place regularlj' and continuous^, as 

 in Batostomella gracilis, James, B. tumida, Phil., Amplexopora 

 cingulata, Ulrich, and many others, or periodically, as in /Stenopora, 

 Lonsdale. The "mature" and "immature" regions arcquite as easily 

 distinguished in the laminar, discoidal, and incrusting zoarium, as in 

 the frondescent and ramose forms. It is, however, not always so easy 

 to detect the two zones in the massive species, since in some of them 

 the walls of the tubes remain thin throughout their length, the 

 diaphragms are remote, and neither interstitial tubes, nor spiniform 

 tubuli are developed. Of such forms Monotrypa undulata, Nich., is 

 a good example, and I confess it is no easy matter to point out the two 

 zones in a species of that nature. However, there are other massive 

 species of the same genus, wherein it is not so difficult, and Monotrypa 



