G. W. Lee — Trepostomata. 
151 
So far only one species of Bcitostomella is known from the Carboniferous rocks of 
the British Isles. 
Genus Leioclema Ulrich. 
Leioclema was erected in 1882 for the reception of Callopora punctata Hall 1 . As it 
has been made to include a large number of species since its publication, it is deemed 
advisable to cite here a recent diagnosis rather than the original one. The diagnosis 
given by Nickles and Bassler 2 is as follows :— 
“ Zoarium ramose, lamellar, subglobose or incrusting ; surface frequently exhibiting 
distinct monticules or maculae ; zooecia with subcircular or irregularly petaloid apertures, 
separated by abundant angular mesopores, which in some species are open at the surface,, 
in others closed ; diaphragms few in the zooecia, abundant, sometimes crowded in the 
mesopores ; acanthopores numerous and strong in the typical species, small and 
inconspicuous in the others.” 
No definite statement appears to have been made by American authors as regards 
the nature of the tabulae, but since all the published figures—including those illustrating 
the internal structure of the genotype, given in Ulrich and Bassler’s “ Revision” 3 —show 
complete tabulae, the genus Leioclema is here understood as possessing complete tabulae. 
In North America Leioclema ranges from the Silurian to the Carboniferous, and is 
one of the most important and prolific of the American Trepostomata. It is therefore 
surprising that only one British representative of the genus should so far have come under 
notice from the Carboniferous rocks, although the conditions prevailing in the British 
area during Carboniferous times were generally favourable to the development of 
the Trepostomata. 
Genus Dyscritella Girty. 
Dyscritella is a name introduced by Dr. Girty, 4 who uses it in a sub-generic sense to 
include two American Lower Carboniferous species having many characters in common 
with Batostomella and Leioclema , but differing from either genus in the absence of tabulae 
in both mesopores and zooecia. 
Beside two species which fall in every respect under the definition given by Dr. Girty, 
the British fauna contains two forms which differ in having a few tabulae in the zooecia. 
As there seems to be a gradual transition from the typical untabulated species to the more 
2 31, p. 33. 
22239 
41, p. 154. 
3 45, pi. xi., figs. 7-9. 
4 11a, p. 193. 
0 
