306 



MISS MCDOIS^ALD AjS'D DE. TEUEMAjS^ OX [vol. IxXVll, 



positions in parallel stocks are distinguished only with difhculty : 

 for instance, carinate species of Procerithiiim of different stocks 

 are extremely similar in general form and appearance. 



Fig, 5. — Diagram showing the retarded development in a species 

 o/* Procerithimn (' Exelissa '), compared tvith the develop- 

 ment ofV. cf. ogerieni. 



«■ ^ 



111. 



VI. 



t 



3 



Vll. 



a b 



a =: Procerithmm cf. ogerieni (Dumortier), Lower Lias, tunnel -lieaps, Old 



Dalby (Leicestershire). A. E. T. colL 

 b = Procerithium (' Exelissa ') cf . numis')nale (Tate), Lower Lias {jamesoni 



zone), Bishop's Cleeve Station, near Cheltenham. L. Richardson coll. 



L.G. 45. 



Still more important is the separation of ' transversal homoeo- 

 morphs.' ^ An example of this class is afforded by Procerithium 

 equireticidatum and P. liassicum ; P. equireticulatum, when 



1 S. S. Buckman, 'The " Kelloway Rock" of Scarborough' Q. J. G. S. 

 vol. Ixix (1913) p. 166. 



