179 
G. W. Lee — Trepostomata. 
digitations of the main walls. They are generally shallow, few reaching the bend 
preceding the final change of direction of the walls. In some portions of the slide 
figured in pi. xvi., fig. 10, they are seen to deviate from their general direction shortly 
after leaving their point of origin. 
In the materials at hand the tabula—seen only in some of the zooecia—are so 
scanty and ill-defined that it is not possible to say whether they are perforate or 
complete. The ratio of axial region to diameter is 0‘5 : 1. 
Seen in tangential sections, the zooecia have occasionally a petaloid outline. A 
number of them are seen to be encircled by a dark ring separated from the zooecial 
cavity by a narrow light-coloured band. The interzocecial spaces are occupied by a 
variable number of unequal-sized, sub-angular mesopores, and by numerous conspicuous 
acanthopores. The latter are mostly of the same size, and often show the central lumen. 
Distribution .—The only specimens which can with certainty be referred to D. miliaria 
are a few metatypes in the Nicholson Collection. They are from Redesdale, Northumber¬ 
land. Nicholson’s statement that the form is common in the Lower Carboniferous rocks 
of Great Britain generally, is not corroborated by the examination of his collection. In 
fact, species possessing mesopores are rather rare in this country. Specimens in the main 
resembling the Redesdale species, but differing in having fewer mesopores, were collected 
by Mr. J. Rhodes in the bed of the river Black Line, opposite Cumcrook, one mile 
S. of Clattering Ford, Cumberland [R. 2679]. 
Observation .—The original of Nicholson’s species was not available, but the foregoing 
description is drawn up from the examination of metatypes in the Nicholson Collection. 
Dyscritella nana sp. nov. 
Plates XIV, fig. 11 ; XVI, figs. 18-20. 
Description. —(a.) External characters. The zoarium consists of small, solid, cylin¬ 
drical, dichotomous branches averaging less than 1 mm. in diameter. There are some 
sixty zooecial apertures along a distance of 1 cm. They are slightly oval and are 
separated by interspaces equal to their own diameter. The interspaces appear either as 
pierced by the minute angular apertures of the mesopores, or as solid, the apertures of the 
mesopores being probably in that case filled by a secondary deposit of sclerenchyma. 
No acanthopores are to be seen. 
(b.) Internal structure. The change of direction from the axial region to the 
periphery is abrupt, and the thick portion of the walls is short and approximately at 
