Foraminifer from the North Atlantic. 503 



attains its full dimensions, tlie neck being of nearly the same 

 diameter as the disk, whilst the upper part is merely rounded 

 off, as shown in figs. 5 and 6 of the accompanying Plate. — 

 G. 0. W.) 



" The shell-wall is essentially vitreous and rather coarsely 

 tubular ; but the tubules become obsolete over and near the 

 sutures, leaving tubuliferous tracts with glassy interspaces. 

 In places the shell grows opaque and sometimes becomes 

 covered with particles of mineral matter or minute Foramini- 

 fera and broken sponge-spicules." 



(Here, then, as in a very large number of the deep-sea 

 Foraminifera, we have the arenaceous structure supplementing, 

 and in some cases entirely superseding, the normally cal- 

 careous shell of the species. 



The older chamber-walls generally appear to be formed of 

 two or even three layers secreted one over the other. Some- 

 times the inner layer is opaque and closely resembles opal glass, 

 the tubules distinctly opening out into the interior. The vitre- 

 ous layer occurs externally to this. In the last-formed and 

 largest chamber the vitreous is the only layer, the tubules 

 then looking like minute white stars with a central pore in 

 each. The disk is quite imperforate. — G. C. W.) 



" Each chamber has a large, transverse, lunular slit in front, 

 this simple aperture being arcuate and forked at one end, as 

 shown in fig. 11. The chambers are superposed, with little 

 or no overlapping for the most part. A secondary coating of 

 shell-wall is here and there seen creeping down the neck 

 towards the glassy base. The basal disk has usually some 

 obscure, minute, opaque lobules about its centre; but thegreater 

 portion of its area is glassy and apparently structureless, the 

 substance presenting the sugar-candy-like aspect so often 

 observable on the bases of the fixed Foraminifera. Even 

 when only one large chamber is present the disk seems to 

 have been already formed ; and it does not subsequently 

 increase in area. 



" In its relation to other Foraminifera, this fungus-shaped 

 form stands between Planorbulina and Glohigerina, and, as to 

 its shell-structure, like Garpenteria. In its semi-opaque condi- 

 tion it imitates the habit of Palvinulina^ which sometimes 

 becomes imperforate over broad tracts, and coated with a- 

 glassy layer perforated by large pores here and there. 



" Instead, however, of spreading out sessile chambers in a 

 compound tent-like arrangement, like Carpenteria^ this sub- 

 cylindrical lobulated Foraminifer raises its chambers high 

 up, with somewhat of a Bulimine twist, on a broad-based 

 peduncle." 



34* 



