84 BRITISH STROMATOPOROIDS. 



investigation has, however, shown, as previously pointed out, that the specimens 

 which we had under examination were "reversed," the skeleton being replaced by 

 calcite. "When viewed from this aspect, it becomes at once evident that Stromato- 

 cerium canadense, Nich. and Mur., is really a Labechia. The genus Stromatocerium, 

 Hall, must therefore be in the meanwhile kept in retentis, until a sufficient inves- 

 tigation shall have been made into the minute structure of the original specimens 

 which Professor Hall had under his observation. 



Genus Rosenella, gen. nov. 



Ccenosteum laminar or massive, with a basal epitheca. Skeleton composed of 

 slightly curved or undulated calcareous plates, which are so combined as to give 

 rise to a series of comparatively large, elongated, lenticular vesicles, upon the convex 

 upper surfaces of which are carried numerous short and rudimentary radial pillars. 

 The radial pillars mostly fall short of the under surface of the lamina next above 

 that from which they spring, and therefore appear merely as conical tubercles on 

 the upper surfaces of the vesicular plates. Definite zooidal tubes are not developed ; 

 but the laminae are porous ; and when the laminse are very thick (as they sometimes 

 are) the pores become converted into vertical tubes, which doubtless lodged 

 zooids. Surface flat or undulated, covered with tubercles. Astrorhizse- not 

 developed. 



As the type of this genus we may take a singular Stromatoporoid (R. macrocystis, 

 n. sp.) from the "Wenlock Limestone of Gotland, of which, through the kindness of 

 my friend Dr. George J. Hinde, I have been enabled to examine specimens. A 

 nearly allied type is the R. (Stromatopora) dentata, Rosen, of the Silurian Rocks of 

 Oesel ; and the form which the same author has described under the name of 

 Slromatopora Ungerni (" Die Natur der Stromatoporen," Taf. ix, figs. 5 and 6), should 

 also be placed here. I am, further, acquainted with two or three undescribed 

 forms of the genus. One of these is a large form from the Ordovician deposits of 

 Ayrshire, which Mrs. Robert Gray has been good enough to submit to me from her 

 unrivalled collection of the fossils of the Palasozoic Rocks of Ayrshire, and which, 

 though in bad preservation, seems to be properly referable to this genus. 



The genus Rosenella is nearly related to Labechia, B. and H., on the one hand, 

 while it has certain striking relationships with Clathrodictyon, Nich. and Mur., on 

 the other hand. "With his usual acumen, Prof. Ferd. Roemer had recognised the 

 relationships of Stromatopora dentata, Rosen, with Labechia, to which genus he 

 had, indeed, transferred the species (' Leth. Pal.,' p. 543). As based upon the 

 type-form, R. macrocystis, n. sp., the genus Rosenella differs, however, from 



