138 BRITISH STROMATOPOROIDS. 



from A. clathratum by tlic much greater delicacy of its general skeletal tissue. 

 The radial pillars are not only straight, and for the most part parallel with one 

 another, but they are very slender. Considerable variations exist, however, in the 

 closeness of the pillars in the specimens which I am disposed to place in this 

 species. The connecting processes or " arms " of the pillars are also exceptionally 

 regular in this species. The specially distinctive feature of A. hebbornense, however, 

 is the unusually complete development of the astrorhizae, as compared with the 

 species of Actinostroma in general. In this respect, the species agrees with A. 

 astroites, Rosen sp., from which, however, it is at once separated by its much 

 coarser skeletal tissue, as well as by other minor characters. The only other 

 species of Actinostroma with which it is necessary to compare the present species 

 is A. intertextum, Nich., but the latter is readily separated by the fact that its 

 skeletal tissue is still more delicate than in A. hebbornense, while the concentric 

 laminae are irregular and sub-vesicular, and the astrorhizae are still more highly 

 developed, and the general form and mode of growth are quite different. 



Distribution — So far as known, A. hebbornense is almost exclusively confined to 

 the Middle Devonian, but it seems to be exceedingly local in its distribution. It 

 occurs in great abundance in the Middle Devonian of Hebborn (Bargatzky's 

 original locality), but I have not found it elsewhere in the Paffrath district, and I 

 have also not clearly identified it from the Bifel. In the Middle Devonian of 

 Devonshire it seems to be of rare occurrence, and I am only acquainted with it 

 from the pebbles of the Triassic conglomerates of Teignmouth. The few Devonshire 

 specimens which I have examined are all highly crystallized, and more or less 

 distorted by pressure (Plate XVI, figs. 13 — 16). I have therefore figured the 

 minute structure of unaltered German examples (Plate XVI, figs. 10 — 12). By the 

 kindness of Dr. Daniel (Ehlert I have been enabled to examine a specimen apparently 

 belonging to this species from the Inferior Devonian of La Baconniere, Mayenne. 



5. Actinostroma intertextum, Nich. PI. XIII, figs. 8 — 11. 



Actinostroma intertextum, Nich. Monogr. Brit. Stromatoporoids, p. 76, fig. 10, 

 188G (figured but not described). 

 Nich. Anu. Nat. Hist., ser. 5, vol. xvii, p. 233, pi. 

 vii, figs. 3 — 6, 1886. 



The ccenosteum has the form of a laminar, more or less circular expansion 

 (PI. XIII, fig. 8), which may reach half a foot or more in diameter, and an 

 inch or more in thickness, and which is covered inferiority by a concentrically 

 wrinkled basal epitheca. The surface is smooth or gently undulated, without 

 " mamelons," but exhibiting fairly developed astrorhizae, the centres of which 



