imperfectly -Icnoion Species of Stromatoporoids. 9 



small thickness, full-sized individuals having a diameter of 6 

 inches or more, with a thickness in the centre of an inch or 

 less. The under surface is covered with a concentrically- 

 wrinkled epitheca. The upper surface exhibits vermiculate 

 and inosculating ridges, formed by rows of elongated tubercles, 

 but is otherwise flat or slightly undulated, showing no 

 "mamelons." Astrorhizae are very imperfectly developed 

 and can sometimes hardly be said to exist. 



In internal structure the skeleton is composed of bent and 

 crumpled concentric laminae, of which about five or six occupy 

 the space of 1 millim. As shown by vertical sections (PI. II. 

 fig. B), the laminee are bent in two ways. In the first place 

 they are bent into numerous chevron-like foldings, no traces 

 of which, however, can be seen on the surface of the coeuo- 

 steum. In the second place each lamina is minutely crumpled 

 or inflected in such a way that the interlaminar spaces are 

 constricted into rows of very imperfect and more or less open 

 vesicles. The radial pillars are developed from the points of 

 inflection of the laminas, but are mostly imperfect and thin. 

 Hence, in vertical sections, the bent and crumpled lamina 

 are far more conspicuous than the radial pillars. Tangential 

 sections (PI. II. fig. 4) exhibit the irregular and vermiculate 

 edges of the transversely- divided and folded laminaj, the cut 

 ends of the radial pillars appearing in these as dark rounded 

 dots. Astrorhizge may sometimes be recognized in tangential 

 sections, but are always inconspicuous. 



Ohs. This beautiful species has certain relationships with 

 G. variolare, Eosen, and specimens occasionally occur which 

 present a mixture of the characters of the two forms. In 

 typical examples, however, G. fastigiatum can hardly be 

 confounded with any other species of Clathrodictyon. It 

 is distinguished from its nearest allies (viz. C. variolare 

 and G. vtsiculosum) by the greater remoteness of the con- 

 centric laminiB and by the peculiar and constant chevron- 

 like and angular folds into which the laminae are thrown. 

 The appearances presented by tangential sections are also 

 exceednigly characteristic, and quite unlike those seen 

 in any other species of Clathrodictyon with which I am 

 acquainted. 



Furmalion and Loccdity. Abundant in the Wenlock Lime- 

 stone of Britain (Dudley, Ironbridge, Much Wenlock, 

 Dormington). I have also collected examples of the species 

 in the ISilurian limestones {^^ Zone of Foitaineriis esthonus^') 

 of Kattentack, Esthonia. 



