18 CANADIAN FOSSILS. 



Locality. — Found in a hard, brownish, calcareous sandstone (Cal- 

 ciferous Sandrock) at Beauharnois, near Montreal, associated with 

 the Ophileta (Maclurea) sordida of Hall. The latter species has 

 much fewer and more rounded whorls, but it is probably of the same 

 sub-genus, as there are intermediate forms connecting this sub-genus 

 with Raphistoma. 



Murchisonia, D'Archiac and DeVerneuil. 



Generic characters. — Murchisonia, DeVerneuil and D'Archiac. Mol- 

 lusca Gasteropoda. Family, Trochidee (see Woodward, 1S5S). 

 Shell elongated, many-whorled ; whorls variously sculptured, 

 and zoned like Pleurotomaria by a spiral band ; outer lip 

 deeply notched ; aperture slightly channeled in front. 



Section 1. — Murchisonia, proper. Turbinate shells, with angulated 

 and variously ornamented whorls, the band generally most 

 prominent; mouth ovate, produced below. 



Section 2. — Hormotoma. Elongate, beaded, with round whorls having 

 a distinct band and notch, as in the other Murchisonia; mouth 

 rounded, not effuse. 



The shells which the above distinguished authors separated under 

 this name, were long classed with Pleurotomaria, with which they 

 are closely allied. They bear the same relation to the Pleurotomaria 

 of the Palaeozoic rocks that Pleurotoma does to Conus; indeed there 

 seems to be an almost perfect gradation between them. If the 

 spire of a Pleurotomaria be lengthened, it becomes a Murchisonia; 

 and, in like manner, if the produced mouth and spire of Murchisonia 

 be shortened, the Trochoid forms so common in the Carboniferous 

 limestone are again produced. 



Probably both these genera are allied to Scissurella, which is not 

 a pearly shell, rather than to the true Pleurotomaria? of the Oolitic 

 rocks, which are nacreous, and clearly allied to Trochus. But we 

 have not the means, in the absence of the operculum, to establish 

 this point. 



Prof. E. Forbes thought the whole group of these thin palaeozoic 

 shells with notched apertures were related to the Ianthinidae. And 

 it is probable this is a correct view, though these could scarcely be 

 pelagic forms, associated as they are with numerous other types of 

 molluscs, annelides, Crustacea, etc., and frequently found gregarious 



