452 THE MOEPHOLOGY OF ' STEPHANOCERAS ' ZIGZAG. 



EXPLANATION OF THE PLATES. 

 Plate XIII, 



Fig. 1. Stephanoceras, a form intermediate between zigzag and 'procerum 

 showing the zigzag-stjle of ornament in the inner whorls and the 

 procerum style of ribbing in the outer whorls. Nat. size. 



2. Outline of aperture. 



3. Stephanoceras suhprocerum, n. f., showing the decrease in size of 



umbilicus. About | nat. size. 



4. Outline of aperture. 



6. Stephanoceras clmisiproceruon, showing greater decrease in size of 

 umbilicus and the greater distance between the obsolescent primary 

 ribs. About | nat. size. 



6. Outline of aperture. 



7. Stephanoceras crassizigzag, var. /8, n. f., showing the change from the 



zigzag-^ijXe to a plain costate ornamentation. Nat. size. 



8. Outline of aperture. 



Plate XIV. 



Fig. 1. Suture-line of a specimen of Stephanoceras zigzag, showing long 

 siphonal, and dependent inner lobes. 



2. Stephanoceras crassizigzag, var. a, n. f., a large specimen showing the 



2'z^2'a^-ornaments retained for a long time, and an exaggeration of 

 the primary ribs on the last whorl. About | nat. size. (This is an 

 important link in the connexion of Bathonian and Bajocian species.) 



3. Outline of the aperture. | nat. size. 



4. Stephanoceras pseudoprocerum, n. f. About f nat. size. (This specimen 



suggests the connexion of zigzag with Macrocephalites.) 



5. Outline of aperture, f nat. size. 



All the specimens figured are from Broad Windsor (Dorset), from the upper- 

 most beds of the Inferior Oolite, representing the zigzag- and possibly part of 

 the fmca-zones. They are rare forms, and were only obtained thanks to the 

 great energy of Mr. Darell Stephens, F.G.S. They are now in my cabinet. 



DiscirssioN-. 



The Peesideistt pointed out that we had long known that Ammo- 

 nites varied in a remarkable way. He considered that there was 

 much to he learned from what might be termed ' pedigree palaeon- 

 tology.' 



Prof. Seeley regarded the paper as important in defining the 

 nature of species and genera. He suggested that similar conditions 

 of deposition had exercised an influence on both persistence and 

 modification of type, in successive periods of geological time. He 

 thought that the same types could in some cases he followed among 

 Ammonites, from the Lias, through the Oxford Clay to the Gault, 

 indicating persistence with modification. The principle of inheritance 

 which had been urged applied, he believed, to Vertebrates and other 

 groups of fossils. 



The E,ev. J. F. Blae:e also spoke. 



The Atjthok, after thanking the Society for the manner in which 

 his paper had been received, remarked that it was absolutely 

 necessary that zones should he subdivided in detail. With regard 

 to genealogy it was only necessary, with a perfect series, to follow 

 out the law of earlier inheritance to ensure correctness. 



