CANADIAN FOSSIIaS. 93 



cki(Z, such as B.strangulata,* B.mutidula, and B. simplex, occur, even in 

 as great numbers, in the rocks of other localities, the Leperditia are 

 not found with them ; tiie latter also occur unaccompanied by these 

 BeyrichicE, L. Caiiadensis itself being found alone in Grande Isle. The 

 close resemblance in outline of some specimens of B. Logani (var. 

 B. leperditioides, fig. -5) to the Leperditice is, I believe, merely a mimetic 

 resemblance of outline, such as we find taking place among many 

 groups, both of the lower and the higher animals. 



b. Var. LABROSA. 

 Plate XI. Fig. 8. 



Length ^, breadth ^V inch. 



The extremities of the valves in this specimen from Hawkesbury are 

 marked by a broad marginal depression, v^hich is contiriued less 

 strongly along the ventral border, and the antero-dorsal corner is 

 more produced than usual. 



This may be an individual modified by accidental circumstances of 

 growth. 



c. Var. LoucKiANA. 

 Plate XI. Fig. 11. 



Specimens of possibly the same species as the foregoing, but of a 

 considerably larger size (often twice as large), occur in two other 

 limestones, specimens of which Sir William Logan has confided to 

 my examination. 



Imbedded in bits of black fine-grained limestone from Louck's Mill, 

 on the Castor River, in the township of Russell, are three glossy black 

 valves, in good preservation, and of different sizes (one specimen being 

 fV in. long and t\ broad, the others being respectively 2^0 in- and -i^ in. 

 in length). In each of these the eye-spot is very distinct, and accom- 

 panied by a local ruggedness of the surface of the valve (not amount- 

 ing to a sulcus) ; the valves are faintly rimmed. 



This black limestone is referred to the Trenton in Geol. Survey 

 Canada, Report, 1851-52, p. 73 ; but, according to a letter of later 

 date from Sir W. E. Logan, it may be Birdseye limestone. 



* Beyrichia strangulata takes on a variety of forms (see Annals of Natural History 

 2nd series, vol. xvi. pi. 6, figs. 18-22) analogous to those of -B. Logani. 



