182 Appendix to Part I. 



distance above the point of separation, the branch is narrow and 

 angular, and traversed along the centre by a ridge, and there is only- 

 one row of cellular mouths on each side. As the branch grew, the 

 ridge widened, and ultimately became celluliferous, a row of mouths 

 springing from its place (inter nata). The three ranges of cellular 

 openings are, in this state of the branch, separated by two ridges, 

 and these, as the development advanced, again widened and became 

 cellular, the five rows being divided by four ridges. This appears 

 to be the extreme stage of growth, another bifurcation taking place 

 immediately after. In the earliest formed part of the cup only two 

 or three rows of mouths prevail ; and where the number is greater, 

 a certain amount of irregularity in the linear arrangement is percep- 

 tible, resulting from the lateral expansion of the branch. 



In the best preserved specimens, the mouths are relatively large, 

 round or oval, and the margin is slightly raised. In the middle 

 rows they are parallel, or nearly parallel, and in the direction of the 

 axis of the branch ; but in the side rows they are often obliquely 

 placed, inclining towards the meshes. In these nearly perfect speci- 

 mens the dividing ridges are thread-like and slightly waved, but 

 there is no trace of the lozenge-shaped compartments so distinctly 

 exhibited in Fenestella ampla. The interspaces between the mouths 

 are flat or slightly convex. In specimens less finely preserved, or 

 deprived of the original surface, the mouths are not uniform in out- 

 line, and have no projecting margin. The diverging ridges are also 

 relatively broader ; and the whole surface, including the transverse 

 connecting processes, is granular or minutely tuberculated. 



The inner layer of the non-cellular surface is sharply fibrous, and 

 the same structure may be more or less clearly detected in the 

 transverse, connecting processes. The number of fibres on the 

 branches do not apparently exceed twelve, and they are in general 

 less numerous. Their range is considerable, additional ones being 

 interpolated as the branch widens ; and their surface is minutely 

 tuberculated. • Xo separate, circular foramina were noticed. The 

 outer layer is uniformly granular, where completed, but every inter- 

 mediate state from the sharply fibrous may be traced on the same 

 specimen. 



No distinct proofs of gemmuliferous vesicles have been observed, 

 but in a specimen, which is believed to exhibit impressions of this 

 species, there are occasionally to be detected, near the mouths, 

 hemispherical casts, perfectly rounded on the surface, and evidently 

 unconnected immediately with the interior of the cells, and which 

 it is presumed may represent those vesicles. Fenestella internata 

 appears to be an abundant fossil, one slab nearly eight inches long 

 and six wide, being covered on both sides with fragments of it," 

 and numerous smaller specimens occur in the collection. The 

 matrix is chiefly a coarse gray calcareous shale, but it is sometimes 

 a splintery limestone, or a hard ferruginous or light-coloured clay- 

 stone. 



