iambe. ] CANADIAN PALAEOZOIC CORALS. Ill 



" Formation and Locality. — Hudson River group ; Snake Island, Lake 

 St. John, Que.; collected by J. Richardson in 1857." (Billings.) 



The types of Zaphrentis Canadensis are from the Hudson River forma- 

 tion of Drummond Island, Lake Huron, and were collected by A. Murray 

 in 1847. A number of specimens, in the museum of the Survey, and 

 labelled Petraia rustica, were collected at Cape Smyth, Lake Huron 

 (Hudson River formation) by R. Bell in 1859. Since then a few specimens 

 were obtained by Commander J. G. Boulton, R.N., at Cape Smyth in 1884. 



A comparison of the types of P. rustica from Lake St. John with the 

 types of Z. Canadensis from Drummond Island and the specimens from 

 Cape Smyth, forces the writer to the opinion that all are the same 

 specifically, and are properly referable to the genus Streptelasma. 



The following description of the species has been drawn from all the 

 available material : — 



Corallum simple, elongate conical, sometimes straight but more often 

 moderately curved near the bottom, expanding slowly from a pointed 

 base, and usually becoming somewhat cylindrical above the midheight • 

 length in mature individuals measured along the convex curve from 70 

 to 90 mm., with a diameter at the top averaging a little over 30 mm. 

 Outer surface rather smooth, transversely ribbed with obscure growth 

 accretions interspersed with finer growth markings. Epitheca complete, 

 with longitudinal septal furrows only faintly^ indicated. Calyx moder- 

 ately deep, with steep sides and a convex floor ; its depth at the side 

 varying in different specimens from about 18 to 25 mm. Septa numbering 

 from about one hundred to one hundred and fifty, the primaries and 

 secondaries alternating, the former passing to the centre, where they are 

 often considerably twisted, the latter very feebly developed ; the primar- 

 ies are very short near the calicular rim, gradually lengthening until they 

 project about 4 mm. from the wall a short distance above the bottom of 

 the cup in the floor of which they reach the centre. Free edges of the 

 septa in the cup denticulated. Dissepiments arched inward to the centre> 

 occupying the interseptal loculi, forming with the twisted inner ends of 

 the primary septa the confused central structure characteristic of Strep- 

 telasma. The dissepiments show a considerable variation in the amount 

 of their development and regularity, they generally rise upward toward 

 the centre forming at the bottom of the calyx a rough convex floor, but 

 less frequently they are more nearly horizontal and less irregular, at which 

 time they may have a Zaphrentine appearance that points to the near 

 relationship existing between the genera Streptelasma and Zaphrentis. 



As regards the illustrations of Z. Canadensis on p. 105 of volume I., 

 Palaeozoic Fossils, it may be said that in figure a the distinctness of the 

 septal furrows is exaggerated and suggests a rough surface not seen in the 



