74 



but in the former the alation of the outer volution is central and appar- 

 ently non-spinose, and the base rather strongly convex exteriorly. In 

 P. Elora the alation of the outer volution is basal and distinctly spinose, 

 and the base flattened around the umbilicus. 



B. Periphery of the outer volution distinctly spinose. 



Pleurotomaria Elora, Billings. 

 Plate 11, figs. 5 and 6. 

 Pleurotomaria Elora, Billings. 1862. Geol. Surv. Canada, Pal. Foss., vol. I., p. 



154, fig. 135. 

 " 1868. Geol. Canada, p. 343, fig. 348. 



This species was described from a very imperfect cast of the interior of 

 the shell collected by Dr. R. Bell at Elora in 1861. A few additional 

 and much more perfect specimens, some of which have most of the test 

 preserved, have recently been obtained by Mr. Townsend at Durham, 

 Elora and at Aboyne, one mile east of Elora. The testifferous specimens, 

 two of which are figured, show that the angulated periphery of the outer 

 volution, when perfect, is armed with a single row of long and slightly 

 curved, slender and hollow spines, not unlike externally to those of Guild- 

 fordia or some recent species of Astralium. In two remarkable specimens 

 collected by Mr. Town-send at Aboyne in 1892, and presented by him to 

 the Museum of the Survey, these spines, as shown by figure 6 on Plate 11, 

 are more than three-quarters of an inch in length. In another specimen, 

 the original of fig. 5 on the same plate, the spines appear to commence on 

 the outer half of the last volution of the spire, where they form a spiral 

 row of small tubercles immediately above that part of the suture which 

 separates the spire from the outer volution, near the aperture, in conse- 

 quence of their being almost completely overlapped by the upper portion 

 of the outer volution. The surface of the apical side of the shell is 

 marked by the usual flexuous strise of growth and that of the spire by a 

 few spiral raised lines, but the markings of the umbilical side are still 

 unknown. 



C. Periphery (as far as known) neither alate nor spinose. 



Pleurotomaria bispiralis, Hall. 



Pleurotomaria hispiralis. Hall. 1852. Pal. N. York. vol. I., p. 349, pi. 84, figs. 2, a-b. 

 Gait, Professor James Hall, 1848 : a single mould of the exterior of 

 the shell. An imperfect and very badly preserved cast of the interior of 

 a shell collected at Hespeler by Mr. Weston in 1867 has since been iden- 

 tified with this species by E. Billings. P. bispiralis appears to be very 

 rare, as these two specimens are, so far as the writer is aware, the only ' 

 ones known. It is recognizable by its narrow turbinate.-conical form, by 

 its imperforate or nearly imperforate base and by its elevated spire, 

 encircled with two spiral ridges. 



