92 BRITISH STROMATOPOROIDS. 



extremely dense, and the formation of the ccenosteum out of successive " lati- 

 laminas," each of which marks a periodic cessation of growth, is also often a con- 

 spicuous feature. Vertical sections (Plate V, figs. 10, 13, 15, 17, and Plate XI, 

 fig. 18) show indistinct parallel radial pillars, more or less wavy and united at 

 intervals by irregular horizontal processes, or by partial confluence with one 

 another. Between the irregular pillars are the vertical but similarly irregular 

 zooidal tubes, usually crossed by very well-developed " tabula?." 



Tangential sections (Plate V, figs. 11, 13, 14, 16, and Plate XI, fig. 16) exhibit 

 a vermiculate and continuously reticulate framework, traversed by the irregular 

 apertures of the zooidal tubes, and thus, but for the absence of " gastropores," in 

 many respects resembling corresponding sections of Mlllepora. Such sections also, 

 as a rule, exhibit extremely well-developed stellate coenosarcal canals or " astror- 

 hizas." As a rule, tangential sections exhibit no traces of the cut ends of the 

 radial pillars, as distinct structures, but such may occasionally be detected. Thus, 

 in well-preserved examples of 8. Beuthii, Barg., from the Devonian Rocks of Ger- 

 many and Britain, the transversely divided ends of the radial pillars can usually be 

 recognised in tangential sections as opaque round masses immersed in the general 

 reticulate tissue of the skeleton (Plate V, fig. 12). The same phenomenon is seen, 

 but less clearly, in some other types. 



The genus Stro?natopora, Goldf., attains its maximum in the Devonian Rocks, but 

 several Silurian species are known. One of the most abundant of the Silurian types is 

 Stromatopora typlca, Rosen, which is apparently not separable from the 8. astroites 

 of the same author, and which occurs in vast abundance in the Wenlock Limestone 

 of Britain and in the Upper- Oesel beds of Esthonia. An allied type is 8. Garten, 

 n. sp., from the Wenlock Limestone of Britain ; and a third interesting form is the 

 Stromatopora discoidea, Lonsd. sp. ( = S. elegans, Rosen), which is found in the 

 Upper- Silurian series of Britain, Gotland, and Esthonia. In the Devonian Rocks 

 of Britain and Germany the type-species, S. co?icentrica, Goldf., is of decidedly rare 

 occurrence ; but 8. Hupschii, Barg., sp., 8. Beuthii, Barg., and 8. bucheliensis, Barg., 

 sp., are all abundant and ckai^acteristic types, while other less completely known 

 forms are also present. 



Qenus Steomatopokella, gen. nor. 



Ccenosteum usually expanded, mostly laminar, and furnished with a basal 

 epitheca; sometimes thin and encrusting. Skeleton imperfectly reticulate, not 

 growing in " latilamina?," or exhibiting such a structure in but an imperfect form. 

 Both the concentric laminae and the radial pillars are comparatively well developed, 

 and are only partially fused to form a reticulate framework. Zooidal tubes are 



