GENUS STROMATOPORELLA. 93 



present, but they are irregular, short, comparatively few in number, and in general 

 but sparingly furnished with tabula?. Astrorhiza? are, as a rule, largely developed, 

 and are commonly intersected by internal partitions or " astrorhizal tabula?;" while 

 they are often superposed in successive interlaminar spaces, in which case the 

 members of each series are connected by one or more vertical canals. Skeleton- 

 fibre minutely porous, or traversed by irregular microscopic tubuli (Plate I, figs. 

 4 and 5 ; Plate XI, figs. 1—4). 



It is difficult to rigidly define the present genus, as in many of its characters it 

 occupies an intermediate position between Stromatopora, Goldf., and Actinostroma, 

 Nich. It agrees with Stromatopora in the minutely porous structure of the 

 skeleton-fibre, in the fact that the skeletal elements are in part fused with one 

 another, so as to form an imperfectly continuous framework, and in the possession 

 of distinct tabulate zooidal tubes. On the other hand, owing to the incomplete 

 fusion of the horizontal and radial elements of the skeleton, there is a considerable 

 resemblance between Stromatoporella and Actinostroma. Thus, in vertical sections 

 (Plate VII, figs. 4 and 6) the concentric lamina? and the radial pillars are usually 

 perfectly recognisable, and are often quite distinct. In tangential sections also 

 (Plate VII, figs. 3 and 5), though we have in part the vermiculate network so 

 characteristic of the Stromatoporids, we likewise observe the detached ends of the 

 transversely- divided pillars, which form so conspicuous a feature in tangential 

 sections of Actinostroma or Glathrodictyon. 



Of the peculiar characters of the genus Stromatoporella, one of the most impor- 

 tant is the nature of the zooidal tubes. In the type-species of the genus (S. 

 granulata, Nich.), the zooidal tubes have the form of short irregular tubes, which 

 often only lead from one interlaminar space to the next, or, at most, to the next 

 space but one, and which are crossed by but few tabula? (Plate II, fig. 10, and 

 Plate VII, fig. 6). In tangential sections (Plate I, fig. 15, and Plate VII, fig. 5) 

 are seen numerous complete or incomplete rings, which represent these irregular 

 zooidal tubes transversely divided. Moreover, the surface (Plate I, fig. 14, and 

 Plate IV, fig. 6) exhibits numerous large- sized tubercles, the centres of which are 

 perforated by round apertures, which we may suppose to have served for the 

 emission of zooids. In Stromatoporella (Diapora) laminata, Barg., the zooidal 

 tubes are more numerous, are longer, and are more richly furnished with tabula?, 

 but the general structure is the same as in S. granulata, Nich. In this species 

 also the surface, in well-preserved examples, exhibits numerous perforated tuber- 

 cles (Plate X, fig. 4) which probably gave exit to the zooids of the colony. 



Astrorhizal canals are also very extensively developed in most of the Stromato- 

 porella}, and are sometimes of very large size (Plate IV, fig. 2). In this genus, 

 the astrorhizal canals are very commonly intersected by irregular partitions, or 

 "astrorhizal tabula?" (Fig. 7, and Plate VII, fig. 3). In some cases, these parti- 



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