251 



plate, Each of these casts of the platform vaults is bounded externally 

 by a short but deeply impressed linear groove, and the groove that 

 represents the median plate extends from the umbo to within a very short 

 distance from the front margin. 



" The only specimen collected is not sufficiently perfect to admit of exact 

 measurements, but the two figures are of the natural size. 



Lower rapid : " one imperfect and slightly distorted cast of the interior 

 of both valves. 



" The specimen would seem to indicate a much smaller species than the 

 preceding, with different markings on the interior of at least one of its 

 valveSj and a much less produced umbo on the brachial valve. It can be 

 scarcely be mistaken for any other American species of Trimerella." 



Stropheodonta (Beachypbion) sp. indet. 



Very similar to the " Sfrophomena Niagarensis " of Winchell & Marcy, 

 the Strophodonta profunda of Hall, as figured and described in the 

 Twentieth Regents Report of the State of New York, but with the surface 

 markings essentially like those of S. varisiriaia, var. arata. Radii thin 

 and distant, with smooth spaces between them. 



Foot of portage road : one well preserved but imperfect ventral valve. 



Plectambonites teansveesalis, Wahlenberg. (Sp.) 



Anomites transvemaZis, Wahlenberg 1821. Act. Soc. Upsaliensis, vol. Ill, p. (54. 



Strophomena elegantula, Hall 1843. Geol. N. York, Rep. Fourth Distr. , 



p. 72, fig. 1. 



Strophomena transversalis, Hall 1«43. Idem, p. 105, fig. 4. 



Leptcena transversalis. Hall 1852. Pal. N. York, vol. II, p. 256, pi. 53, 



fig. 5. 

 „ Billings 1856. Canad. Nat. &. Geol., vol. I, p. 138, pi. 



2, figs. 14 (fe 15. 



Plectambonites area & tcnera, Shaler 1865. Bull. Mus. Comp. Zoo]., vol. IV, p. 64. 



Plectambonites transversalis. Hall & Clarke.. 1892. Pal. N. York, vol. VIII, pt. I, p. 298, 



pi. 15, figs. 34-36. 



Foot of portage road : two imperfect but characteristic ventral valves. 



In the Museum of the Survey there are specimens of this species from 

 the Clinton and Niagara formations at Grimsby, Dundas and Hamilton, 

 Ont.; from Divisions 2, 3 and 4 of the Anticosti group, four miles west of 

 Jupiter River, at East Point, and at the Jumpers, Anticosti ; also from the 

 Silurian (Upper Silurian) rocks at Lake Temiscouata, N. B. 



Orthis, sp. indet. 



Upper rapid ; one half of the ventral valve of a very small, rather 

 coarsely ribbed and probably undescribed species of Orthis, allied to 0. 

 Davidsoni. 



