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Paleozoic Corals and Foraminifera. 9 
gitudinally, and obsoletely wrinkled concentrically : vertical 
section, middle area occupied by slightly irregular transverse 
diaphragms extending across two-thirds the diameter of the 
tubes, about four in the vertical space of one line, their edges 
abruptly bent downwards ; lateral areas very narrow, of equal 
width, the inner composed of one set of minute horizontal 
plates, the outer of two rows of minute, curved, vesicular plates 
inclining upwards and outwards. 
_ This species differs from the D. concinnum (Lonsd.) of the 
carboniferous limestone east of the Ural chain, in the great pro- 
portional width of the transverse medial plates, which average two- 
thirds the diameter of the stem, or three times the width of the 
_ two outer areas of one side in the present species, but average one- 
third the diameter of the stem, or about equal to the two outer 
areas of one side in the other. The dichotomous mode of divi- 
sion of the stems characteristic of this group, and also the conical 
upward projections of the centre of the transverse lamellz im- 
mediately under the point of fissure, were very well shown in 
many of the specimens. 
Abundant in the carboniferous limestone near Corwen. 
_ (Col. University of Cambridge.) 
Stylastrea irregularis (M‘Coy). 
Sp. Char. Corallum of polygonal (five- or six-angled) tubes two 
lines in diameter, of such twisted and irregular upward growth 
that a vertical fracture frequently exposes a mixed appearance 
of outer walls and imternal section ; outer surface longitudi- 
nally striated and transversely wrinkled by waves of growth: 
vertical section, immer area broad, regularly septate by nearly 
_ straight, equal, thick transverse plates ; outer area very nar- 
row, composed of much-curved vesicular plates, forming rather 
open rounded cells, in rows obliquely upwards and outwards, 
two or three in a row: horizontal section, central area smooth, 
surrounded by about thirty slightly flexuous radiating lamelle 
from the walls, fifteen of which are much shorter than the 
others ; near the walls the radiating lamelle are connected by 
few, thick, vesicular plates. 
This species is remarkable for the peculiar, irregularly twisted 
mode of growth of the columns, which, when the rock is com- 
pact, gives the mixed character to the fracture seemingly between 
that of Lithostrotion (Strombodes) and Stylastrea. It 1s also re- 
markable for the nearly perfect transverse chambering of the 
central area. The small diameter of the tubes and few lamelle 
easily distinguish it from the other allied species. 
