46 PROCEEDINGS OF THE ACADEMY OP [1886. 



which, beginning from a solid basal leaf, densely crowded with 

 papillose prominences, delicate versiculous plates are formed at 

 short intervals, connecting into a floor which bridges over 

 the tops of these papilli, which are prolonged until another 

 floor spreads over their apices, and until from six to twelve of 

 these subordinate laminse had formed, inclosing between them 

 versicular cell-spaces. Then after an evident interruption in the 

 uniform progress of growth, a new one of the larger layers com- 

 posed of subordinate laminte, commenced to form on top of the 

 other. The pillars intersecting the laminae subordinate to a larger 

 bandlike layer form uninterrupted columelles which usually 

 correspond with those of the next succeeding layers or bands. 

 In other cases, however, the columellse or pillars of each one of 

 the thicker compound lamince are independent in their position, 

 and do not correspond. Some of these pillars are often much 

 stouter than the others, and divide into several mammiform side 

 branches. The majority of them are simple, rounded, or later- 

 ally compressed into vermicular crests, particularly so in the 

 circumference of the monticulose prominences of the surface, 

 where these crests radially converge towards the centre, resem- 

 bling the horizontal radially converging channel expansions of an 

 ordinary Stromatopora^ but in this case it is the tissue-mass, and 

 not the intervening furrows, which produces the vermicular 

 radiating converging lines. The interstitial cell-spaces inclosed 

 between the convex transverse leaflets bridging over the space 

 from pillar to pillar, are very similar to the convex vesicules in 

 a vertical section of a CystiphyUum. As above stated in the 

 majority of specimens occurring abundantly in the Trenton 

 group of Escanaba River, and at Nashville, Tennessee, and 

 also in the drift of Ann Arbor and in the upper part of the 

 Cincinnati group at Madison, Indiana, the actual skeleton sub- 

 stance is almost completely destroyed, and its place filled with 

 crystalline carbonate of lime. It often occurs that several of the 

 thick bandlike layers are composed of a succession of vesiculose 

 layers twice or three times the size of the vesicules composing 

 other layers of the same specimens. In this case the vertical 

 pillars become very obscure, so that the whole appears as an 

 indiscriminate accumulation of vesicules as large as those of an 

 ordinary CystiphyUum. 

 The surface of Stromaiocerium was not known to Messrs. 



