161 



Three forms which may be classed as varieties of this species are the 

 following : 



Variety BENEPUNCTA. PL XII., fig. 16. 

 Can. Rec. Sci. Montreal, 1900, Vol. VIII., p. 449. 

 Anterior cardinal curve longer than the posterior ; anterior marginal Variety 

 curve straightened and the greatest width of the valve posterior to the 

 middle. Hinge-line nearly half of the length of the valve (2 mm). 

 Ocular tubercle 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. Another example, more oval and more 

 tumid, has an obscure row of tubercles 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. 



Sculpture. The surface is corroded, but on the posterior slope of the 

 valve are anastomosing ridges parallel to the margin. 



Size. Length, 4 mm. ; width, 3 mm. ; depth of a valve, 1 mm. 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^EVIS. 



Can. Rec. Sci. Montreal, 1902, Vol. VIII., p. 450. 



Oval, cardinal curves long, the anterior one rounded. Hinge line more Mutation 

 than half the length of the valve ( ), a tubercle at the posterior end. described. 

 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. 



Sculpture. Punctuation 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. b, and E 2 c, Lower 

 Etcheminian, at Dugald brook. 



11 c. R. 



