TALiEOZOIC CORALS AND FORAMINIFERA. 1"^ 



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 fom* 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 lamellae 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.) 



Stylastraa 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 internal section ; outer surface longitudi- 

 nally striated and transversely wrinkled by waves of growth : 

 vertical section, inner 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 lamellae 

 from the walls, fifteen of which are much shorter than the 

 others ; near the walls the radiating lamellae 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 [Stromhodes) and Stylastraa. It is also re- 

 markable for the nearly perfect transverse chambering of the 

 central area. The small diameter of the tubes and few lamellae 

 easily distinguish it from the other allied species. 



