191 



writer, those of the spire rounded, the outer one rounded, ventricose, 

 much broader than high, and higher than the spire : suture distinctly- 

 defined. 



Surface, as indicated by a gutta percha impression of a natural mould 

 of the exterior oLthe test, marked with numerous, extremely fine (or thin) 

 spiral raised lines or minute ridges. On the dorsal side of the outer 

 volution, when viewed with a lens, these ridges are seen to be unequal in 

 size, the larger ones usually alternating with one or two smaller ones. 

 There are about twenty of the larger ridges in this region, and these, 

 although placed rather close together, are not quite equidistant. On a 

 cast of the interior of the shell there are indications of Ihe larger revolving 

 ridges, and in addition to these there is a faint narrow spiral groove, 

 with an obtuse peripheral carination immediately under it, which may 

 represent the slit-band, at about the midheight of the outer volution. 

 On the surface of the gutta percha impression, however, the middle of 

 the supposed slit-band, when viewed with a lens, is seen to be en- 

 circled with a minute spiral ridge. 



Maximum breadth of the specimen described, six millimetres ; probable 

 height of the same, when perfect, about equal to the breadth. 



Inmost Island, Kinwow Bay, Lake Winnipeg, D. B. Dowling and L. 

 M. Lambe, 1890 : an imperfect but well preserved cast of the interior of 

 the shell and a sharply defined natural mould of the exterior of the same. 

 The figure on Plate 20 is drawn from a gutta percha impression of this 

 mould. 



Although many of the spiral lines on this mould are so small as to 

 be invisible without the aid of a lens, no clear indications of any of 

 the lines of growth can be detected. It is quite uncertain whether the 

 shell was really provided with a slit-band or not, and consequently 

 whether it should be referred to Pleurotomaria or Cyclora. Its shape is 

 not very unlike that of Cyclora rainuta, Hall, as figured by Meek,* but 

 the surface of that species is described and represented as smooth. 



LiospiRA Americana, Billings. (Sp.) 



Pleurotomaria lenticularis. Hall 1847. Pal. N. York, vol. I., p. 172, pi. 37, 



fig5. 6, a-d. 

 Pleurotomaria Americana, Billings 1860. Canad. Nat. and G-eoI., Vol. V., p. 



164, fig. 7. 



.1 „ 1863. Geol. Canada, p. 184, fig. 179. 



i(os/Ji>a ..Imencana, Ulrich and Scofield .... 1807. Geol. Minn., Final Rep., vol. III., 



pt. 2, p. 996. 



A few casts of the interior of shells of this species were collected at 

 Punk Island by Professor H. Y. Hind in 1858 ; at Oat Head and at Inmost 



* Geological Survey of Ohio, Paleontology, vol. I., p; 152, pi. 13, figs. 7, n-e. 



