450 Canadian Record of Science. 



distinct ; a shallow furrow behind and below it. A faint 

 ridge extends forward from the posterior end of the hinge 

 half way to the furrow below the ocular tubercle. Ano- 

 ther example, more oval and more tumid, has an obscure 

 row of tubercules arching outward and forward from the 

 posterior cardinal angle to the anterior cardinal curve. 

 A low ridge extends back from the ocular tubercle to the 

 hinge. 



Soujjfure. The surface is corroded, but on the posterior 

 slope of the valve are anastomosing ridges parallel to the 

 margin. 



Size. Length 4imm ; width 3|mm ; depth of a valve Inim. 

 A carapace from this locality had length 4^ mm ; width 

 3^ mm ; depth of the two valves 3 mm. 



Horizon and locality. Assise E. 1. d., Lower Etcheminian, 

 at Boundary Brook, Scarce. 



Mutation L^.vis, n. mut. 



Oval, cardinal curves long, the anterior one rounded' 

 Hinge line more than half the length of the valve (f ), a 

 tubercle at the posterior end. Ocular tubercle off from 

 the hinge-line and prominent ; ocular furrow shallow. The 

 right valve has a thread-like marginal fold ; no fold on 

 the posterior slope of the left valve. 



Scid]3ture .Punctation fine, showing anastomosing ridges 

 near to and parallel to the posterior slope of the valve. An 

 example from the higher horizon shows a thickened band 

 near the margin along the posterior marginal slope, that 

 bears obscure elongated tubercles. An example of the 

 mould from the same horizon has three small pits behind 

 the ocular tubercle, parallel to the hinge. 



Size. Length 4^mm ; Width 3^ mm ; depth 1 mm. 



Horizon and locality. Occurs in assises E. 1. h, and E. 2. 

 c, Lower Etcheminian, at Dugald Brook. 



The following are measurements of examples from the 

 two horizons : 



