﻿PARALLELOPORA GOLDFUSSII. 191 



Distribution. — S. discoidea, Lonsd. sp., is entirely confined to the Silurian Rocks, 

 and has hitherto been recognised only in the Wenlock Limestone of Britain, 

 and in corresponding deposits in Northern Europe. In the Wenlock Limestone 

 of England the species is moderately common, occurring at Ironbridge, Much 

 Wenlock, and Dudley; but really well-preserved examples are rare. In the 

 Wenlock Limestone of Wisby (Gotland) 8. discoidea appears to be a common 

 species, the specimens from this region being usually highly mineralised, but 

 commonly having the surface well preserved. In Esthonia the species has 

 hitherto been recognised only at the single locality of Kleiue Ruhde, occurring in 

 limestones belonging to the zone of Pentamerus ehstonus. 



Genus 2. — Parallelopora, Bargatzhy, 1881. 



(Introduction, p. 95.) 



1. Parallelopoua GoLDFussri, Bargatzhy. PL XI, figs. 7 — 9; and PL XXV, 



figs. 4—9. Woodcuts, figs. 22, 24, 



and 25. 



Paeallelopoea G-oldfussii, Bargatzky. Die Stromatoporen des rheinischen 



Devons, p. 63, 1881. 



Coenosteum irregularly spheroidal or clavate, from 2 to 7 cm. in diameter, 

 with a limited basal attachment, and apparently devoid of an epitheca. 

 The mode of growth is not distinctively latilaminar, and the concentric laminae 

 are simply curved, the surface being free from " mamelons." Where ob- 

 served, the surface shows a moderately coarse reticulation, with oval, rounded, or 

 vermiculate pores representing the mouths of the zooidal tubes ; or it may be 

 partially covered by an apparently imperforate calcareous membrane. 



Astrorhizge are present, but are variably developed, being sometimes small 

 •and inconspicuous, and at other times composed of large, few-branched canals. 

 In the latter case the astrorhizse are exceedingly irregular in their distribution, 

 being abundant in some specimens and nearly absent in others. The horizontal 

 canals of the astrorhizge are often furnished with oblique or transverse calcareous 

 partitions (" astrorhizal tabulae"); and are sometimes connected with compara- 

 tively large, rounded or oval internal cavities, which are scattered through the 

 coenosteum, and are also furnished with calcareous partitions or tabulae. These 

 cavities are not always present, and may possibly be connected with reproduction, 

 thus representing the " ampulla? " of the Hydrocorallines. 



As regards its internal structure, the skeleton-fibre of Parallelopora Goldfussii 



26 



