imperfectly-known Species of Stromatoporoids. 325 



of connecting-processes, Syringostroma ristigouchense re- 

 sembles an Actinostroma, while in the minutely porous 

 structure of the skeleton-fibre it entirely resembles a typical 

 Stromatopora. The only closely allied form with which the 

 present species could be confounded is Syringostroma nodu- 

 latum, Nich., from which it is distinguished by the more 

 dense character of the skeletal network and the fact that the 

 laminae are not so undulated as to give rise to astrorhizal 

 eminences. 



Formation and Locality. Silurian (Lower Helclerberg for- 

 mation ?), Dalhousie, New Brunswick (coll. J. W. Spencer 

 and Oeol. Survey of Canada). 



Syringostroma nodulatum, Nich. 

 (PI. X. figs. 5-7.) 



Stromatopora nochdata, Nicholson, Paleontology of Ohio, vol. ii. p. 249, 

 pi. xxiv. tigs. 3-3 b (1875). 



The ccenosteum in this species is massive, splitting readily 

 into thick concentric strata. The laminae are sharply undu- 

 lated, so as to give rise to prominent conical astrorhizal 

 eminences or " mamelons," the summits of which are rounded 

 and are placed about 12 millim. apart (PI. X. fig. 7). The 

 astrorhizae themselves are fairly developed, but their branches 

 are small and rapidly become lost in the general skeletal 

 network. They are disposed in vertical systems, each system 

 being provided with a small wall-less axial canal, which 

 opens at the summit of one of the " mamelons " just spoken of. 



Vertical sections (PI. X. fig. 6) show that the skeleton is 

 composed of strong radial pillars, which have a minutely 

 porous structure and are disposed at right angles to the undu- 

 lated " concentric laminae." About six or seven pillars occupy 

 the space of 2 millim. measured transversely. The concentric 

 laminae are regularly undulated and are closer together where 

 they bend upwards to form the mamelons than in the con- 

 cavities between the latter. 



Tangential sections (PI. X. fig. 5) show the cut ends of the 

 transversely divided pillars, often more or less angular in 

 outline, united together by a comparatively small number of 

 delicate connecting-processes. The spaces between the cut 

 ends of the pillars are comparatively wide and irregular, and 

 represent sections of the zooidal tubes. 



Obs. This species agrees with the preceding in combining 

 in its ccenosteum the general structure of an Actinostroma 

 with the minutely porous skeleton-fibre of a Stromatopora. 

 It is most obviously separated from S. ristigouchense, Spencer, 



Ann. d- Mag. N. Hist. Ser. 6. Vol. vii. 23 



