76' 



with a small piece of the test preserved, collected by Dr. R. Bell at Elora 

 in 1861. No other specimen of it has been seen by the writer. In addi- 

 tion to the original description it may be added that the umbilicus of the 

 type of P. Deiopeia is so narrow that it is most probable that the base of 

 the shell is imperforate when the test is preserved. 



Pleurotomaria Hercyna, Billings. (Sp.) 



Murchisoiiia Hercyna, Billings. 1862. Geol. Surv. Canada, Pal. Foss., vol. I., 



p. 158, fig. 141. 



Gait, E. Billings, 1857 : two casts of the interior of the shell, one of 

 which has a portion of the test preserved. Elora, T. 0. Weston, 1867 : 

 two similarly preserved specimens. According to Professor Lindstr m,* 

 the Murchisonia Hercyna of Billings comes near to Pleurotomaria 

 elliptica, Hisinger, and may possibly be only a variety of that species, 

 though the Canadian shell is more elongated, and its apical angle is more 

 acute. The characters of M. Hercyna, on the whole, seem certainly to 

 accord better with those of Pleurotomaria than with those of Murchisonia. 



" Pleurotomaria '? Viola," Billings. 



Plate 12, fig. 2. 

 Pleurotomaria? Fioto, Billings. 1865. Geol. Surv. Canada, Pal. Foss. , vol. I, p. 169. 



Gait, E. Billings, 1857 : a badly preserved cast of the interior of the 

 shell, with nearly the whole of the spire buried in a compact crystalline 

 dolomite, and showing little more than the general shape of the broadly 

 and very deeply umbilicated base. This specimen, which is the type of the 

 species, and which has not been figured before, is the original of the 

 drawing reproduced on Plate 12. Elora, D. Boyle, 1880 : a cast of the 

 interior, with the basal portion only exposed. Belwood, J. Townsend, 

 1886 : two similar specimens. 



This species is so imperfectly characterized that it is very doubtful if it 

 can be retained. No specimen has yet been collected in which even a 

 very small piece of the test is preserved, or any considerable portion of 

 the spire is visible, and the outer volution of the type, as described by 

 Billings, shows only " some appearance of an angulation." It is by no 

 means certain, even, that the species should not be referred to Strapa- 

 rollus rather than to Pleurotomaria. 



*0n the Silurian Gastropoda and Pteropod a of Gotland. Kongl. Svenska Vetens- 

 kaps-Akad. Handl., vol. XIX., No. 6, Stockholm, 1884, p. 106. 



