Cambrian Rocks in Cape Breton 441 



If there is any meaning in these furrows that extend 

 from the hinge as indicating muscular attachment there 

 is a sugestion of a posterior muscle, towards the posterior 

 end of the cardinal line in the depression that exists there 

 in Beyrichona and Hipponicharion, and is faintly shown 

 in Escasona. But of such posterior muscle we have no 

 sure evidence. Of the anterior adductor muscle, however, 

 there are plain indications on the interior of many valves. 



It is clear that Ostracods having such a radical dif- 

 ference of structure from those others of a later time, must 

 have had different habits of life, and among other peculiar- 

 ities noted is that they usually occur solitary. Seldom do 

 we find any aggregations of individuals and never the 

 swarms on a single layer of rock that may be found in 

 occurrences of the later Ostracods ; hence they appear not 

 to have possessed in any marked degree the gregarious 

 habit of these later: genera. 



Another peculiarity of the Etcheminian and Protole- 

 nian forms, as distinguished from the prevalent Ostracoda 

 of Ordovician and Silurian lime, is the unusual convexity 

 of the front moiety of the valve as compared with the 

 other. This for some time led the author to be uncertain 

 as to which was the anterior end of the valve in the genus 

 Beyrichona. He, however, now has no longer any doubt, 

 as the related genus Bradoria, with its prominent ocular 

 tubercle sets this matter at rest, and shows that the thick 

 end of the valves is the anterior one. 



Another common feature is the prevalence of species 

 which are as wide or wider than long. This peculiarity is 

 connected with a long hinge line and with more or less 

 • abrupt cardinal curves of the margin, before these merge 

 into the true anterior and posterior margins of the valves 

 (see Plate I. figs. 1 to 6, a & &). When the angle at the 

 lower end of these cardinal curves is acute, a tubercle is 

 sometimes developed, in addition to that which marks 

 the anterior and often the posterior end of the hinge line 

 (PI. I. fig.13, a & c. 



