Vol. 67.] 



THE AVONIAN OF BUEEINGTON COMBE. 



375 



abuts sharply against a vertical wall, built up of vertically elongated 

 vesicles (represented diagrammatically in the figure). 



As might be anticipated from the uniplanar curvature, the 

 symmetry of the young cornute stage is essentially bilateral ; on 

 the other hand, that of the adult cylindrical stage tends to become 

 radial. 



Fig. 11. — Contoured plan of one of the characteristic tabula? of 

 Caninia patula, Mich. X 2-7 diameters. {Drawn from silicificd 

 specimens occurring in y at Burrington Combe.) 



[The outer ring of vesicles is diagrarnrnatically shown, and the septa 

 are omitted.] 



The ranging of this gens under Caninia rather than under 

 Cyathophyllum is a matter of personal preference, for it cannot be 

 maintained that so typical a Cyathophyllum as C. mwchisoni does 

 not occasionally exhibit both a distinct fossula and stereoplasmic 

 thickening. The most characteristic feature, however, of Cyatho- 

 phyllum — the presence of a marginal ring of small vesicles within 

 \ the central area — is lacking in Caninia patula. On the other hand, 

 the development of an amplexoid stage — so distinctive a feature of 

 Caninia cornucopia? — is also lacking in Caninia patula. 



It is impossible to consider C. patula to have been derived from 

 either C. cornucopia? or C. cylindrica, and in my opinion its marked 

 peculiarities warrant the creation of a new genus. 



