WHITEAVE8. ] FOSSILS OF HAMILTON FORMATION OF ONTARIO. 401 



A small specimen of a shell which Mr. Schuchert identifies with this 

 species was collected b3' him in 1895 at Bartlett's Mills (in the " Lower 

 third of the section "). This specimen, which is No. 20,485 of the United 

 States National Museum Catalogue of Invertebrate Fossils, is about four- 

 teen lines in length, or height, and has most of the test preserve.!, although 

 somewhat pyritized. Three specimens of essentially the same size and 

 shape, but with little or no portion of tlie test preserved, had previously 

 been found, one at Bartlett's Mills by the Rev. Hector Currie, and the 

 others near Thedford by J. Townsend and G. Kernahan. 



Pleurotomaria Arkonbnsis. (N. Sp.) 

 Plate 48, figs. 12 and 12 a. 



Shell depressed turbinate, nearly twice as broad as high and flattened 

 below. 



Volutions six, the first four forming a moderately elevated .-^ubconical 

 spire, the last two almost step-shaped, and much more rapidly expanding 

 laterally. Outer volution depressed, flattened next to the suture, 

 then sloping obliquely dov^fuward, above, and truncated at the periphery : 

 its surface marked by a spiral row of minute rounded tubercles, of uniform 

 size and closely contiguous, above the slit-band, and by a similar row of 

 tubercles below io ; the upper row being placed about half way between 

 the suture and the slit-band, and the lower one on the lower or anterior 

 margin of the periphery. Slit-band placed on the outer edge of the apical 

 side of this volution, and bounded by two minute and parallel spiral 

 ridges, the outermost of which constitutes the upper or posterior margin 

 of the periphery. Umbilicus apparently of moderate width in casts of 

 the interior and rather narrow when the test is preserved, but all the 

 specimens that the writer has seen have most of the umbilical sui'face 

 covered by the matrix. 



The foregoing description is based upon two specimens collected at 

 Bartlett's Mills, by Mr. Kernahan, in 1895, both of which are now in the 

 Museum of the Survey. One of these, which is figured, has the test 

 preserved, and the other is a mere cast of the interior of the shell. The 

 former, which is twenty millimetres in its maximum breadth, and about 

 eleven mm. high, has most of the umbilical side covered with the matrix, and 

 the flattening of the base is perhaps abnormal. A worn cast of the interior 

 of a shell, which is probalily referable to this species, in the Museum of 

 the Survey, is labelled " Hamilton formation. Township of Plympton, A. 

 Murray," and a similar but unworn cast was found at Thedford, a few 

 years a^o, by the Rev. Hector Currie. In each of these casts the outer 



