HISTORICAL INTRODUCTION. 11 



throughout ; lamellar system indicated by the radiate arrangement of the vermi- 

 cular passages, which commonly diverge from the summits of little eminences 

 raised in the concentric laminas. 



" Species : C. pustuloswm, G. monticuliferum, G. granuliferum, G. pohjmorphum, 

 G. radiosum, G. ramosum. 



" Genus, Gaunopora (Philhps). — c Corallum polymorphous, composed of minute, 

 irregular, vermicular, cellulose tissue, disposed in obscure concentric layers, tra- 

 versed by a few long, larger, variously disposed, vermiform, cylindrical channels ' 

 (M'Coy, « Brit. Pal. Foss.,' p. 06). 



" Species : G. placenta, G. ramosa, G. verticillata. 



" Genus Stromatopora (Goldf.). — Polypi confluent, with individualities sensibly 

 obliterated. Corallum consisting essentially of confluent diaphragms, or con- 

 centric layers, which generally inclose a foreign body — being secreted on all sides 

 of it, and forming a spheroidal mass. 



" Species : S. concentrica, 8. striatella, 8. nux, 8. rugosa, 8. compacta, 8. num- 

 mulitisimilis." 



With regard to the two new genera proposed by Professor Winchell in the 

 above-quoted synopsis, Idiostroma is an exceedingly abnormal form, and the 

 absence of figures illustrative of the minute structure may sufficiently explain why 

 the type has not been recognised by subsequent observers. The type of the genus, 

 viz. I. cmspitosum, Winch., is described as resembling a large cgespitosely-branched 

 Cyathophylloid Coral, forming masses three or four feet in diameter, composed of 

 stems which vary from one fifth to one third of an inch in diameter, and which 

 may be either apart or in contact with another. The exterior is " longitudinally 

 vermicular-striate." The transverse section " exhibits a radiating structure, as in 

 the GyathophylUdcB ; but there is no outer wall or definite limitation to the struc- 

 ture, and the interior is completely filled with concentric circles of coralline 

 substance except a small perforation in the centre." In the absence of a more 

 detailed account of the minute structure, it would, as above remarked, be difficult 

 to decide positively as to the true relationships of this singular type. I have, 

 however, collected a number of specimens from the Devonian Limestone of Hebborn, 

 in the Paffrath district, which seem to be unquestionably congeneric with Idiostroma 

 caispitosum, Winch. ; and I shall subsequently give a description of the characters 

 of the genus as elucidated by these examples. 



The genus Gmnostroma, Winchell, on the other hand, comprises Stromatoporoids 

 of the normal type, and the only really distinctive feature in the diagnosis of the 

 genus, as given by its founder, is the presence of " astrorhizae," or radiately dis- 

 posed canal-systems (the "polypi" of Winchell's definition). As will be subse- 

 quently seen, however, such stellate canals are developed in a large number of 

 Stromatoporoids, in which the minute structure is otherwise exceedingly different ; 



