160 BRITISH STROMATOPOROIDS. 



Tangential sections (Plate XX, fig. 2 ; and Fig. 18, A) show that the radial pillars 

 are hollow, each being traversed by a well-marked axial canal. The tissue forming 

 the periphery of the pillars (Plate XX, fig. 3) is composed of very delicate laminae, 

 which surround the axial canal concentrically, and which often show a minute 

 cribriform structure. The connecting-processes spring from this tissue, and can 

 commonly be followed in vertical sections for a considerable distance into the 

 substance of the pillars. Tangential sections further exhibit irregular dark lines 

 connecting the transversely divided radial pillars ; these lines are the cut edges of 

 the vesicular plates or processes which fill the intervals between the pillars. 



There is, apparently, a complete absence of definite zooidal tubes or surface- 

 apertures, and the " concentric lamina? " of the ordinary Stromatoporoids are 

 represented solely by the vesicular tissue which unites the pillars together. 



L. conferta differs from the L. oMoensis, Nich., of the Ordovician Rocks of North 

 America in the fact that the radial pillars are of larger size, the surface-tubercles 

 being correspondingly bigger, while the interstitial vesicular tissue is of a coarser 

 type and is present in smaller amount. In its general external appearance 

 L. conferta nearly resembles the Lophiostroma (Labechia ?) Schmidiii l of the 

 Silurian Rocks of the Island of Oesel ; but the surface-tubercles of the latter are 

 much larger, while the internal structure appears to be wholly different. 



Distribution. — Labechia conferta appears to be wholly confined to the Silurian 

 Rocks (Upper Silurian of Murchison). It is a common species in the Wenlock 

 Limestone of Britain, occurring at Ironbridge, Dudley, Dormingtou, Longhope, 

 &c. I have also specimens from the Wenlock Limestone of Gotland (collected by 

 Prof. Lindstrom) ; but the species has not been recognised as occurring in the 

 Silurian Rocks of Esthonia or Oesel. 



2. Labeohia scabiosa, n. sp. PI. XX, figs. 4 — 6. 



Coenosteum forming a small discoid expansion, with a concentrically striated 

 basal epitheca (Plate XX, fig. 5). The upper surface is flat, and is covered with 

 irregular tubercles, which are usually multiple and are mostly placed from \ to 



1 Labechia ? Schmidtii was described by me at some length in the ' Annals and Magazine of 

 Natural History,' ser. 5, vol. xviii, 18S6. Judging from its apparent structure it cannot be referred to 

 the genus Labechia, and I propose for it the generic name of Lophiostroma. The genus is characterised 

 by the possession of a laminar coenosteum, composed throughout of sharply undulated, closely approxi- 

 mated, and exceedingly thin calcareous lamellae. The upward bendings of these lamellae give rise to a 

 series of spurious pillars, the superior extremities of which appear on the surface as prominent 

 tubercles, while the downward bendings correspond with the interspaces between these. The under 

 surface is covered with a concentrically-striated epitheca. 



