1886.] NATURAL SCIENCES OF PHILADELPHIA. feiJ 



of the successive laminae and their interstices round these 

 vertical columns, is also brouglit forward as a noteworthy 

 circumstance. It is likewise stated that radiating channel 

 expansions may be present or not. I had described and figured 

 these two forms in my paper, under the name Stromatopora 

 Wortheni^ thinking a division into two species superfluous, as 

 insensible gradations from one form into the other exist. 



The columellar streaks, seen to intersect the mass of this other- 

 wise typical form of Stromatopora in vertical sections, are pro- 

 duced by the repeated abrupt flexions of the lamellae imo 

 papillose prominences which cover the surface, similar to those 

 we observe in many other forms of Stromatopora, as for instance, 

 in Str. pustulifera Winchell. 



As in this latter form, the prominences are somewhat larger 

 and consequently the flexions are not so abrupt, and as the tissue 

 of this form is throughout more compact, we do not observe an 

 obvious contrast between the density of the parts corresponding 

 with the papillose prominences and the broader downward-curved 

 intermediate portions of the skeleton, while in the so-called 

 Stylodictyon, the abrupt flexions of the lamellae in the papilli 

 into an almost vertical direction, cause the closer approxima- 

 tion, and consequently greater density, of these parts than of 

 the intermediate gently downward -curved portions of the 

 laminated skeleton which have comparatively open, well-defined 

 interlaminar cell-spaces conti'asting with the denser portions, so 

 as to let them appear under the form of vertical columns. 

 Examining transparent vertical sections of such specimens, we 

 see that the lamellae are not interrupted in their continuity while 

 passing across these columellar streaks, and that no additional 

 tissue element comes into play, which could be claimed as con- 

 stituting the substance of the columelles. On the contrary, 

 every portion of these columellar streaks is identifiable either 

 as a normal part of the lamellae or of the intermediate system 

 of pillars. To mention among the generic characters the 

 concentric arrangement of the lamellae and their interstices 

 round these columellar centres, appears to me rather superfluous, 

 as it is a necessary consequence of the monticulose prominences 

 into which the surface is raised. I could invariably observe in 

 all specimens of this tribe which came under my observation, 

 radial horizontal ducts, which, by the Authors, are said to be 

 sometimes developed and sometimes not. 



