118 PROCEEDINGS OF THE ACADEMY OP 



la, of similar structure to those of the former genera, are sometimes noticed 

 in specimens of Fistulipora. The central opening appears to have been closed 

 in some of the opercula by a subsequent solid deposition; we find, at least in 

 all the perfect opercula, the central portion forming an offset from the sur- 

 rounding marginal part. 



Fistulipora is quite polymorphous ; we find its species incrusting, and in 

 free expansions, with orifices on one side only, or in double leaves, with ori- 

 fices on both sides ; they grow in hollow stems, or in strumose cystical form, 

 or in solid ramifications, or in undefined large masses. 



One, or several, of these forms are generally significant for a certain species. 

 but I think, in the systematic arrangement of the Bryozoa, too much weight 

 has been given to their external form and to the manner in which they grow. 



For further elucidation of my general remarks, I will append the descrip- 

 tion of a number of species of Fistulipora which are new, or whose anatomy 

 was not fully recognized before. 



Hbllipora (Constellaria) antheloidea, 



Is the oldest and at the same time the most marked form of Fistulipora. 



Its circular tubules with projecting rims, the vesiculous interstitial cell- 

 mass, the monticulose maculae with a star-like depressed cellulose centre, re- 

 present, in ideal perfection, the principal characters of the genus. 



In this place I take occasion to mention a lower Silurian fossil, whose nature 

 is only imperfectly known, and which resembles in its structure Fistuli- 

 pora. 

 Stromatocerium kugosdm Hall. 



By its external appearance, it has been generally confused with Stromato- 

 pora, but this latter has a widely different structure and belongs to the Petro- 

 spongiae. 



Slromntocerium rugosum grows in large subglobose masses with an undula- 

 ted monticulose surface. Vertical sections show a series of superimposed 

 laminae, on which the naked eye can scarcely recognise organized structure; 

 under the magnifier we find it composed of small, subparallel, simple tubules, 

 and of a comparatively coarse vesiculous cell- mass surrounding the tubules. 

 These cell-vesicules are convex above, concave below, spread out in horizontal 

 layers, and not in vertical rows ; the size of the vesicules is very unequal and 

 varies from a half to one millimeter in the horizontal direction, about half as 

 much in the vertical sense. 



Diameter of tubules one-sixth of a millimeter ; distance between each other 

 about half a millimeter. 



The more delicate surface characters cannot be recognized, on account of 

 the unfavorable state of preservation of the specimens. 



According to Hall, it is found in the Black River limestone. My specimens 

 are from Madison, Ind., where it occurs in association with Favistella stellala, 

 in the upper strata of the Hudson River group formation. Some of the best 

 specimens, however, I found in the drift deposits of Michigan. 



The Clinton group, and, in particular, the Niagara group, contain a good 

 many species of Fistulipora structure tue Trematoporas of Hall. 



In regard to a few of them, I have to make some remarks. 



Trematopora tubulosa of the Clinton group, and Diamesopora dichotoma of the 

 Niagara group, combine exactly the same internal structure with their 

 external similarity of form. 



The inner face of their hollow steins is covered by a delicately-wrinkled 

 dermatic crust. Their tubules are arranged in oblique rows, becoming some- 

 what irregular by the slightly-developed maculae. The basal portions of 

 the tubules are prostrate, and in immediate contiguity; but, by abruptly 

 bending up to the surface, leave a more or less considerable space between 

 the erected tube ends, which is filled out by cellulose tissue. This cell-mass 

 is generally found homogeneous, and allows no discrimination of cells. A 



[May, 



