326 Prof. H. A. Nicholson on some new or 



by the possession of exceedingly well-marked conical or 

 rounded astrorhizal prominences or " mamelons," due to the 

 close and sharp undulations of the laminae. It is also sepa- 

 rated from the latter by the smaller thickness of the radial 

 pillars and the more open character of the skeletal network 

 thence resulting, the comparatively small number of con- 

 necting-processes, the less perfectly circumscribed zooidal 

 pores, and the less completely developed astrorhizae. 



Formation and Locality. Devonian (Corniferous Limestone), 

 Kelley's Island, Ohio. The above description is based on a 

 fragment of the original specimen described {coll. Geol. 

 Survey of Ohio). 



Syringostroma densum, Nich. (PI. X. figs. 8 and 9.) 



Syringostroma densa, Nicholson, Palaeontology of Ohio, vol. ii. p. 251, 



pi. xxiv. figs. 2-2 b (1875). 

 Syringostroma densum, Nicholson, Mon. Brit. Strom, p. 97, pi. xi. 



figs. 13 and 14 (1886). 



The ccenosteum in this species is probably massive ; but 

 fragments have the form of irregular lamina?, with a dense 

 and close texture. The concentric laminae of the skeleton are 

 gently curved, but do not give rise to superficial eminences or 

 " mamelons." The astrorhizse are of large size, with ramified 

 and inosculating horizontal branches. 



Vertical sections (PI. X. fig. 9) show numerous close-set 

 and irregular radial pillars of small size having a minutely 

 porous structure and united by irregular connecting-processes 

 in a partially reticulate manner. The general tissue thus 

 formed is traversed at intervals by radial pillars of much 

 greater size than the normal. About ten to twelve small 

 pillars are found in a space of 2 millim. measured trans- 

 versely, while the large pillars are about 1 millim. apart. 

 Vertical sections also show conspicuously the large rounded 

 apertures representing the transversely divided horizontal 

 canals of the astrorhizse. 



Tangential sections (PI. X. fig. 8) show a general closely 

 reticulated tissue of a minutely porous character, in which 

 the cut ends of the smaller radial pillars are only with diffi- 

 culty or not at all recognizable as distinct structures. This 

 network exhibits at irregular intervals rounded dark masses of 

 comparatively considerable size, representing the cut ends of the 

 large radial pillars above spoken of. Tangential sections also 

 show the inosculating astrorhizal canals and the minute and 

 irregular sections of the zooidal tubes. 



Obs. My material of this remarkable Stromatoporoid being 



