CANADIAN FOSSILS. 11 



umbilicus as greatly exposed as in Ophileta. All are Lower Silurian 

 forms, and from near the base of the system, and all, with the excep- 

 tion of Scalites proper, which does not occur in the Ottawa limestone, 

 are illustrated in plates 2 and 3. 



The genus must be regarded, in the present state of our knowledge, 

 as allied to Rleurotomaria and Murchisonia (which, with Scissurella, is 

 now considered* to belong to the Trochidae), but differing from 

 them importantly in the want of the spiral band. It is probably 

 nearer to Ianthina, some of the typical species of which are strongly 

 striate in the direction of the lines of growth, and deeply notched in 

 the middle of the mouth. These thin floating shells certainly seem 

 to offer the best affinity with Scalites and its various sub-genera ; 

 and inasmuch as Ianthina is arranged as a family close to the Trochidae 

 and Haliotidae, the association of Scalites with the former would not 

 call in question its relationship to the latter. Both Ianthina and 

 Scalites have but few whorls and a short spire (in the fossils with a 

 much greater tendency to a depressed shape) ; while the Trochidce 

 and Murchisonia are on the contrary elongate and many-whorled. 



The total absence of opercula, while it rather strengthens this 

 view of the affinities of Scalites, throws some doubt on the propriety 

 of keeping Murchisonia among the Trochidse. Professor E. Forbes 

 would have arranged all these thin-notched shells, with Platyschisma 

 (McCoy), and some other palaeozoic genera, alongside of Ianthina. 



Eaphistoma. 



I have altered but little the essential parts of Prof. Hall's descrip- 

 tion of the genus. The main characters by which the sub-genus is 

 distinguished are pointed out by him, viz. : the close-fitting sutures 

 between the whorls, and the subtrigonal, not rounded, form of the 

 mouth, caused by the production of the outer angle. 



There are two sections even of this sub-genus, one with flat spire 

 and the whorls convex below (R. striata, Hall), the other with spire 

 and base about equally convex, and a general lenticular form 

 ( R. staminea, Hall, R, Unticularis, Sowerby, &c). The two species 

 here described belong to the second sub-division. 



* By Mr. Woodward, the author of the " Rudimentary Treatise on Recent and Fossil 

 Shells." John Weale, London, 1854. This excellent work contains in a condensed 

 form the fruits of much research, and is highly prized by European naturalists. 



