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



differ from one another in the fundamental character of the solid 

 or porous condition of the skeleton-fibre, while the connecting- 

 processes of the radial pillars are markedly different. 



Formation and Locality. The typical Canadian specimens 

 of A. fenestratum are from dolomitic limestones of Devonian 

 age, " Pentamerus Point," Lake Manitoba. These are non- 

 infiltrated examples ; but the minute structure of the skeleton- 

 fibre has been affected by crystallization, the axial canals of 

 the radial pillars being thus more or less entirely obliterated. 

 Less typical examples, in an infiltrated condition, occur in the 

 Devonian rocks of Lake Winnipegosis. These have a finer 

 structure and less highly developed astrorhizse than the typical 

 examples from Lake Manitoba ; but their state of preserva- 

 tion does not admit of their being satisfactorily separated from 

 the latter. 



Svringostroma ristigouchense, Spencer. 

 (PI. VIII.' figs. 6-8.) 



Ccenostroma ristiqouchense, Spencer, Bull. Univ. of the State of Mis- 

 souri, p. 49, pi yi. figs. 12, 12 a (1884) . 



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

 figs. 11 and 12 (1886). 



The ccenosteum in this species is massive, more or less 

 definitely latilaminar in growth, and readily splitting into 

 thick strata concentric with the surface. The lamina? are 

 gently curved, and there are either no astrorhizal eminences 

 (" mamelons ") or but very inconspicuous ones. Astrorhizas 

 are as a rule very well developed, being of large size and much 

 branched ; they are arranged in vertically superimposed 

 systems, and have their centres about 1 centim. apart. 



Vertical sections (PI. VIII. fig. 7) show the skeleton to be 

 composed of thick, close-set, parallel, radial pillars, which are 

 minutely porous in structure. The radial pillars are separated 

 by narrow zooidal tubes, about five or six pillars occupying a 

 space of 2 millim. measured transversely, while about seven 

 " concentric lamina? " occupy the same space measured 

 vertically. Tangential sections (PI. VIII. figs. 6 and 8) 

 show the large rounded ends of the transversely-divided radial 

 pillars, placed close together and united in a stellate manner 

 by whorls of delicate radiating connecting-processes or 

 " arms." The rounded or sinuous pores included within the 

 " hexactinellid " network thus formed represent the zooidal 

 tubes as seen in section. 



Obs. In the fact that the ccenosteum consists of well-deve- 

 loped radial pillars, united at corresponding levels by whorls 



