1902] Whiteaves — On the Genus Panenka. 265 



specimens from the Detroit River by a new specific name, and 

 they may therefore be provisionally named and described as 

 follows. 



Panenka Canadensis (sp. nov. ). 

 Shell, or rather cast of the interior of the shell, of about the 

 averag-e size, valves regularly and rather strongly convex, varying 

 in outline in different specimens from subcircular to longitudinally 

 subovate, but always at least a little longer than high. Posterior 

 side rather broader and much longer than the anterior, umbones 

 broad, tumid, prominent, very oblique and placed considerably in 

 advance of the midlength, beaks curved inward and forward ; 

 hinge line straight, horizontal, considerably prolonged behind in 

 some specimens but apparently not so much so in others. 



Test unknown ; surface of the cast marked by numerous 

 (about sixty) narrow but prominent ribs, with concave grooves 

 between them. In the original of figure i on Plate XV, the ribs 

 are slight'y unequal in size. Most of them are simple but they 

 occasionally bifurcate, and here and there a few shorter ribs are 

 intercalated between the longer ones, that radiate from the um- 

 bones. In the original of figure 2 on the ^ame Plate, the ribs are 

 more regularly disposed, and they are all a little larger posteriorly 

 than anteriorly. 



Muscular impressions and hinge dentition unknown. 



Dimensions of a comparatively high and short specimen 

 (fig. i); maximum length 74 mrn., greatest height (inclusive of 

 the umbo) 67 mm.: do. of a more elongate specimen (fig. 2) that 

 is narrower in the direction of its height, length 77 mm.; greatest 

 height, which happens to be behind the umbo, 60 mm. 



Corniferous formation, Anderdon township, Essex county, 

 Ontario : a few specimens collected by Mr. Harry Hodgman, U. 

 S. Inspector, in October and December, 1901. According to Mr. 

 Nattress they are from a brown dolomite which underlies the true 

 Corniferous limestone in that neighbourhood. 



Explanation of Plate XV. 

 Panenka Canadensis. 



Fig'. 1. — Side view, natural size, of a right valve of a Specimen with sub- 

 circular marginal outline, and comparatively long hinge line 

 behind. 



Fig. 2. — Similar view of the right valve of a longitudinally subovate specimen, 

 with a comparatively short hinge line. 



Both of these specimens are in Mr. Hodgman's collections. 



Ottawa, Feb. 15th, 1902. 



