165 



The relation of the muscle scar to the ocular tubercle is also a means of 

 discriminating the genera in these early forms of Ostracoda : thus in 

 Bradorona (Fig. 2) and Bradoria (Fig. 5) it is diagonally behind and below 

 the tubercle, but in Beyrichona it is below and somewhat in front of the 

 tubercle. In Hipponicharion (Fig. 4) the muscle print presses in 

 behind and below the tubercle. In Indiana (Fig. 1) the scar though not 

 well recognized appears to be as in Bradorona (Fig. 2). In Escasona 

 neither muscle scar nor tubercle have been certainly identified. 



Comparing this group of genera with those of the Ordovician and Radically 

 Silurian, we note some obvious differences from them. Perhaps the most 

 notable is the way in which the visual and muscular organs are crowded at ti 

 the front end of the hinge. This would exclude them from the great 

 family of the Leperditidse, Jones, in which the muscle scar is near the 

 middle of the valve. The lateral expansion of the valves also is charac- 

 teristic, and still more the way in which a number are pointed at the 

 middle of the ventral margin. 



We see no nearer relation in these species to the " zoe " group of giants 

 described by Barrande, than to the Leperditidse ; these remind one more 

 of the bivalve carapaces of Phyllopod crustaceans. The Canadian forms, 

 though many are above the average size of the fossil Ostracoda, are far 

 inferior in this respect to Aristozoe and its allies. 



It seems to the writer that the position of the main adductor muscle 

 scar separates these species from all described Ostracoda, and he would 

 suggest for them the designation Bradoriidse, taking as types the genera 

 Beyrichona and Bradoria. Hipponicharion is widely divergent from the 

 others and in its strongly ridged surface simulates Beyrichia and may for 

 the present be placed in the family Beyrichidse. 



LEPERDITIA ? ? EUGOSA. PI. XII, fig. la to c. 



(Can. Rec. Sci., Montreal, Vol. VIII., p. 443. 1902.) 



This species may prove to be of another genus when more numerous Leperditia ? ? 

 examples are found. The single example found does not seem to justify 

 a final reference to any described genus. 



Only the right valve is known and this is rather flat, and flattened 

 toward the hinge and the posterior slope ; its greatest convexity is in the 

 middle and the lower third. The outline is broadly oval, with a hinge 

 line half of the length of the valve. The anterior and posterior cardinal 

 curves are long ; the posterior marginal curve and the lower side of the 

 valve are both somewhat straightened, and the anterior marginal curve 

 strongly rounded. 



