SOME NEW DEVONIC FOSSILS 



283 



of Sowerby's well known Upper Siluric O r t h i s h y b r i d a . 

 In its immature stages it is essentially that shell ; at full growth 



J ^ J 



Rhipidomella hybridoides 



its characters have changed by progression and indicate thereby a 

 Postsiluric age. 



Loiver Devonic. Dalhousie, N. B. 



Rhipidomella numus nov. 



A shell directly comparable to R. (Or this) oblata Hall 

 of the Helderberg fauna, agreeing therewith in form and contour 

 of valves though perhaps never attaining the size of that species. 

 It differs therefrom : ( 1 ) in the slightly greater length of hinge, 

 but principally (2) in the very much coarser and sparser plication 

 of the surface. In R. oblata the radial striae are fine and 

 crowded; in a typical example I find about 70 at a distance of 10 



Rhipidomella numus 



mm from the beak and at the anterior margin in a shell 32 mm 

 long, 190. In the largest example of R. n u m u s, 24 mm long, 

 there are 40 at 10 mm from the beak, 106 at the margin. Thus 

 there are practically two striae in R. oblata to every one in 

 R. numus; those of the latter angular, multiplying rapidly. 

 When compared with the rarer Helderberg species R. eminens, 

 its plication is still much coarser, its hinge not so long and it lacks 

 the elevated ventral beak of that shell. 



The species is quite abundant. 



Lower Devonic. Dalhousie, N. B. 



