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BRITISH STROMATOPOROIDS. 



As regards its microscopic structure, the most marked feature in 8. granulata 

 is the presence in tangential sections (Plate I, fig. 15, and Plate XXVI, fig. 1 a) 

 of more or less numerous, complete or incomplete, rings, enclosing each a central 

 space. These represent the perforated tubercles of the successive laminse, as seen 

 when transversely divided. The same feature characterises corresponding sections 

 of 8. Selwynii, Nich., also ; but the latter species is sufficiently separated from the 

 present form by its comparatively coarse structure. 



From S. eifeliensis, Nich., the present species is distinguished by its non- 

 parasitic habit of growth, by the much more limited development of the astrorhizee, 

 by the presence of " mamelons " or astrorhizal prominences, and by the possession 

 of the perforated tubercles alluded to above. 



The form which I shall here describe under the name of 8. solitaria is nearly 

 related to 8. granulata, as shown by its similar mode of growth, its possession of 

 "mamelons," and the general likeness of the minute structure of the skeleton in 

 the two. It also exhibits in tangential sections (Plate XXVII, fig. 6) appearances 

 very similar to those which are above referred to as characterising corresponding 

 sections of S. granulata. At the same time 8. solitaria is sufficiently proved to 

 be distinct from 8. granulata by its decidedly coarser structure, and also by the 

 much more complete development of " astrorhizal cylinders," while its skeleton 

 resembles that of 8. eifeliensis in being tubulated rather than simply porous. 



From 8. socialis, Nich., the most abundant of the British species of Stromato- 

 porella, the present species is distinguished by its generally thicker skeleton- fibre, 

 and more lax structure, as well as by the characteristic perforated tubercles pre- 

 viously referred to. Lastly, 8. damnoniensis, Nich., is adequately separated from 

 8. granulata by its much coarser skeleton-fibre, as well as by the limited develop- 

 ment of its astrorhizal system. 



I have not so far met with any example of 8tromatoporella granulata in the 

 " Caunopora-state." Indeed, one of the difficulties in arriving at absolutely clear 

 and satisfactory conclusions as to the so-called " Caunoporee " is that " Caunopora 

 tubes " are so commonly present in certain Stromatoporoids, while there are a 

 few forms — apparently of very similar structure and habit — in which such tubes 

 are seemingly never present. 



Distribution. — Not uncommon in the Devonian rocks (Hamilton formation) of 

 Ontario. As above stated, no undoubted British or German examples of this 

 species have been recognised as yet ; but the microscopic structure of some of 

 the Stromatoporellse which abound in the pebbles of Devonian Limestone in the 

 Triassic conglomerates of South Devon strongly reminds us of this species. 



