154 BRITISH STROMATOPOROIDS. 



Dormington. I have also collected examples of this species in the Silurian (" zone 

 of Pentamems esthonus ") of Kattentack, Esthonia. By the kindness of Mr. 

 Whiteaves, I have also been enabled to examine specimens of this species belonging 

 to the collection of the Geological Survey of Canada. The specimens in question 

 are from Glenelg Township, near Durham, Ontario, and occur in a Magnesian 

 Limestone belonging to the Guelph formation. 



13. Clathbodictyon confebtum, n. sp. PI. XVIII, figs. 13 and 14. 



Ccenosteum massive ; the base, surface, and mode of growth unknown. The 

 growth is by means of " latilamince," each of which is composed of excessively 

 close-set concentric lamina?, which are so inflected as to form with the radial 

 pillars an exceedingly fine vesicular tissue (Plate XVIII, fig. 13). The concentric 

 lamina? seem to be incompletely developed, and tangential sections show simply a 

 minute reticulation, interspersed with minute dark dots and lines (Plate XVIII, 

 fig. 14). Astrorhizae appear to be wanting. 



I have hesitated greatly in founding a distinct species for this form, as I have 

 only a single incomplete example of it, which I owe to the kindness of my friend 

 the late Mr. Champernowne, and its state of preservation is exceedingly poor. In 

 spite of this, there seems to be no reason to doubt that we have to deal with a species 

 of Glathrodictyon, of the type of G. vesiculosum, and G. variolare ; and a special 

 interest thus attaches to the specimen, as no other example of a Glathrodictyon^ of 

 this type has hitherto been detected in the Devonian Rocks in Britain. In its 

 general aspect this form approaches in fact very closely to G. vesiculosum, but its 

 skeletal tissue is even finer than in the latter. Vertical sections, indeed, show 

 simply a congeries of excessively small cells arranged obscurely in lines, and 

 disposed in successive strata or " latilaminee " of a millimetre in thickness, or 

 thereabouts (Plate XVIII, fig. 13). Owing partly to its fineness, and partly to its 

 very poor state of preservation, I have found it impossible to make reliable measure- 

 ments of the number of interlaminar spaces in a given space. Moreover, the 

 concentric laminae do not seem to be so well developed as in G. vesiculosum, and 

 the general structure is therefore more thoroughly vesicular than is the case in the 

 latter species. The same feature is observable in tangential sections. Another 

 character which distinguishes it from C. vesiculosum is the apparent absence of 



1 Among some fossils submitted to me for examination from the Devonian Rocks of Trance by Dr.. 

 Daniel (Ehlert, I find more than one form of Glathrodictyon. One of these approaches very close to 

 C. vesiculosum, Nich. and Mur., which is so characteristic a type in the Silurian Rocks. The specimen 

 in question is found in tbe Devonian deposits of St. Jean, Laval, Mayenne. 



