59 



that of the species now under consideration : while the hinge plate of the 

 corresponding valve of M. Greenii is much narrower in proportion to its 

 size. 



Rhinobolus Galtensis, Billings. (Sp.) 



Plate 15, fig. 2. 

 Obolus Oaltensis, Billings 1862. Geol. Surv. Canada, Pal. Foss., 



vol. I, p. 168, fig. 152. 

 Trimerella minor, Dail 1871. Am. Journ. Conch., vol. VII., p. 



83. 



Rhynobolus ? (Compare Obolus Oaltensis, 



Billings) Hall 1871. Twenty third Rep. Reg. N. Y. St. 



Cab. Jfat. Hist., p. 247, pi. 13, fig. 10, 



and expl. of that plate. 

 Obolellivn Galtensis, 'B.iWingi 1871. Can. Nat. and Geol., vol. VI., 



N. S., p. 222. 



1872. lb., pp. 327-329. 



Trimerella ? Galtensis, Davidson & King. .1874. Quart. Journ. Geol. Soc. Lond., 



vol. XXX., p. 151, pis. 18, fig. 13, and 



19, figs. 4 and 4 a. 

 Rhynobolus Qalten-iis, Whiteaves 1884. This vol., pt. 1, p. 7, pi- 8, fig. 3, 



and perhaps pi. 2, fig. 1 a, but not pi. 



8, fig. 3 a. 

 Rhinobolus Galtensis, Hall & Clarke 1892. Pal. N. York, Vol. VIII., pi. 4B, 



and explanation of that plate. 



The original description of Obolus Galtensis, Billings, is as follows : 

 " Ovate, both valves moderately convex ; sides gently, and front margin 

 broadly rounded ; apical extremity of ventral valve 70° ; greatest width 

 a little below the middle. The area of the ventral valve is flat, with a 

 concave groove along the middle ; and while in one specimen it lies 

 nearly in the plane of the margin, in another it slopes a little outwards. 

 The largest specimen seen is 25 lines in length and 18 in width. 

 Locality and Formation. — Gait. In the Guelph formation ; Middle 

 Silurian. Collectors : E. Billings, R. Bell." In a paper " On the Genus 

 Obolellina," published in the Canadian Naturalist and Geologist for 

 April, 1872, Mr. Billings adds the following particulars: "The beak of 

 the ventral valve is very large, its length being one-half that of the body 

 of the shell. It is slightly incurved. The area has three furrows, the 

 peduncular and the two lateral grooves. The muscular impressions are 

 rhomboidal rather than ovate, and confined to the central portion of the 

 shell. There are no cavities under the area." 



While writing the paper last mentioned Mr. Billings states that " fifteen 

 casts of the interior of 0. Galtensis " were lying before him, but the 

 specimens in the Museum of the Survey upon which the foregoing 

 descriptions of that species would seem to have been most largely based, 



2 



