442 Canadian Record of Science. 



These laterally expanded valves are in a number of 

 species pointed at the lower margin and in most the ven- 

 tral margin is more or less angulated (PI. I figs. 2, 3 and 6). 

 It thus admits of division into two portions which may be 

 designated the anterior and posterior curves {e and d), 

 according to whether the part of the margin indicated is 

 in front or behind the ventral angulation. Sometimes the 

 anterior curve of the margin will be stronger as in Beyri- 

 chona (Fig. 3) (and Escasona? Fig. 6), sometimes the post- 

 erior curve, as in Indiana (Fig 1) and Bradorona (Fig. 2), 

 is the stronger. In Hipponicharion (Fig. 4) the two are 

 about equal, 



The cardinal curves (Pl.I.figs. 2 etc., a and h,) extend 

 from the hinge line along the margin until it becomes at 

 right angles to the hinge, and they also vary greatly in 

 direction and extent. Thus in Indiana (Fig. 1) the post- 

 erior one is long, the anterior shorter ; in Bradorona (Fig. 

 2) they are approximatively of equal length ; in Beyri- 

 chona (Fig. 3), sp. ^9ct2?^/^o, the posterior one is almost obso- 

 lete but in other species {tinea, 'plctna.ia, etc.,) of this genus, 

 it is well shown, and with these the species of Escasona 

 (Fig. 6) agree. In Bradoria (Fig. 5) both cardinal curves, 

 and especially the posterior are well shown. In Hipponi- 

 charion on the contrary these curves are almost obsolete. 



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 Bra- 

 doria (Fig. 5) it is diagonally behind and below the tuber- 

 cle, 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 Indi- 

 ana (Fig. 1) the scar though not well recognized appears 

 to be as in Bradorona (Fig. 2). In Escasona neither mus- 

 cle scar nor tubercle have been certainly identified. 



Comparing this group of genera with those of the Ordo- 

 vician and .Silurian, we note some obvious differences from 



