352 PALAEONTOLOGY OF ILLINOIS. 



The primary orifice is of sub-circular form, somewhat nar- 

 rower than the width of the cell, and occupies the anterior 

 third (or a little more) of its length. As growth proceeded the 

 front of the cell was gradually thickened by a deposit of lami- 

 nated sclerenchyma ; this calcareous addition being built up 

 about the orifice so as to draw it out into a vertical tubular 

 shaft, called the "vestibule" by Mr. Vine. The superficial aper- 

 ture is circular, and, with few exceptions, surrounded by a peri- 

 stome. 



In transverse sections of the branches the original basal or 

 germinal plate is generally quite distinct from the subsequently 

 added layers of calcareous tissue. A number are figured on 

 plates LIV and LY, that show how sharply the plate is often dis- 

 tinguished. Almost invariably the lower side of the plate pre- 

 sents a number of tooth-like projections that represent transverse 

 sections of former longitudinal striations. It is a fact that the 

 reverse of many Fenestellids show strong striae on very young 

 examples, which are wanting or nearly obsolete on old specimens. 



description and figures of Glauconome marginalis, for which they proposed the new 

 subgenus Diplopora, upon the ground that there is a small secondary pore immedi- 

 ately beneath the true apertme. Similar secondary pores they mentioned as oc- 

 curring in their Glauconome (Acanthopora) stellipora and Fenestella (Actinostoma) 

 fenestrata. This secondary pore I consider the result of attrition combined with 

 a paucity of calcareous secretion by the zooids. The Messrs. Young and Young 

 show in their figure of the first that the supposed pore varies much in size, and rightly 

 attribute the variation to the state of preservation. Had they investigated a little far- 

 ther, I think they would have seen that there is a good reason for the presence of the 

 "pore" in their species. These (especially D. marginalis) are forms in which the de- 

 posit of cal areous material over the primitive cell was much less than usual. Polypora 

 whitei and var. sevillensis are likewise such forms, and, as will be seen from fig. Ib 

 and 2 on plate LXII, frequently present what Waters suggests might be compared with 

 the suboral pore found in so many CHILOSTOMATA. I am really sorry that I flnd it so 

 often necessary to differ with my esteemed English collaborers in this difficult branch 

 of palseozoology. Indeed, in this instance I am particularly grieved, since it would have 

 pleased me much to be able to corroborate so important a point for comparison be- 

 tween Pateozoic and Recent Bryozoa. But, being convinced that their conclusion is 

 based upon defective specimens, I must dissent. 



Comparing examples of the several species in question with shallow tangential sec- 

 tions of ordinary Fenestellids we find that with a little diagrammatic restoration of the 

 section, there is no essential difference, while the supposed "pore" is explained by the 

 wearing away of the thin and slightly convex 1 portion of the front of the cell. The dark 

 matrix which has entered the cell is then clearly seen, and the weathered portion might 

 readily be mistaken for a suboral pore. The thin septum which is said to separate the 

 lower from the true aperture is nothing more or less than the superior hemiseptum, 

 and when the attrition has proceeded to the extent that even this is removed then the 

 general appearance of the cell with its two inflections looks precisely like what we see 

 in tangential sections of most FENESTELLIDS. 



