178 
G. W. Lee — Trepostomata. 
The acanthopores are conspicuous. They occur generally at the junction-angles, and 
owing to the thinness of the walls project into the cavities of the zocecia and mesopores. 
Their centre does not show a lumen, but is much darker than the peripheral portions. 
Tangential sections show that the mesopores do not form more than a single row 
between the zocecia, and occasionally the zooecia are in juxtaposition without any 
mesppores intervening. 
Distribution. —The above description is based on the examination of several specimens 
discovered by Prof. S. Reynolds, of Bristol, and kindly lent by Dr. T. F. Sibly. 
They are from the basement beds (K 1 zone) of the Carboniferous rocks of the Avon 
section, and occur with Cleistoporci and Productus bassus Yaughan. 1 This species has 
not so far been met with from other localities. 
Observations.—Leioclema avonense is the only British Carboniferous species of 
Leiodema yet found, and does not appear to be closely related to any of the numerous 
American species of this genus. 
It is interesting to note that—so far as ascertained—the size of the present species 
is apparently greatly in excess of that generally attained by the other members of 
the genus. 
Genus Dyscritella Girty. 2 
Dyscritella miliaria (Nicholson). 
Plate XVI, figs 9, 10. 
1881. Monticulipora tumida , var. miliaria Nicholson. The Genus Monticulipora 
and its Sub-Genera, p. 123, pi. iii., fig. 2. 
Description. — (a.) External characters. The zoarium consists of solid cylindrical 
branches from 2 to 4‘5 mm. thick. Some forty-five zooecial apertures occur along'a distance 
of 1 cm. Their outline is circular. They are never in contact, being separated by a 
variable number of minute sub-angular mesopores. Maculae of mesopores are not 
uncommon. The acanthopores cannot be seen, even with a strong lens. 
(b.) Internal structure. The peripheral portion of the zooecia-walls is greatly 
thickened and at right angles to the long axis of the zoarium. The most conspicuous 
feature of longitudinal sections is the large number of mesopores, which appear as 
1 From information kindly supplied by Dr. Sibly. 
2 A diagnosis of the genus is given on p. 151. 
