1876.] 371 [Hyatt. 



the growth, on the other hand, is not affected, the increase in size 

 being even greater proportionally than in the normal Humphriesia- 

 num forms leading into the macrocephalum group. Upon the whole, 

 the old age or degradational changes which precede death in the 

 individual, are found to be correllative with the products of degrada- 

 tional changes in every direction, whether they result in producing 

 a discoidal form, like Bayleanum, a flattened form, like Steph. planu- 

 lum, or a smooth form, like the last described variety of contraction. 1 

 Above the Bath formation the history of this series is fragmentary; 

 the few specimens I have seen present, for the most part, the broad 

 abdomened coronatum form. The forms sometimes referred to this 

 series from the White Jura I do not think can be properly designated 

 as descendants. Quenstedt analyses this question very fully in his 

 diagnosis of the convolutus group, p. 578 of Der Jura, and it is also 

 my impression, derived from careful examination of closely allied 

 forms, that even such apparently coronatum-like forms as the Graresi- 

 anum, figured by D'Orbigny, pi. 219 of Terr. Jurassique, will be 

 found to belong to the convolutum or planulatum group, and that the 

 true coronali have no representatives in the White Jura. 



The extraordinary form, Steph. subkeve, to which we now come, 

 presents in its adult condition so close a resemblance to the Amm. 

 Goliatlius that Quenstedt is evidently in " Der Jura" doubtful of its 

 true affinities, though he had previously, in " Die Cephaloden," re- 

 ferred it to the coronatum group. The development, however, shows 

 none of the peculiar variations observable in the Amm. Goliatlius 

 group, and the young in some specimens retain the coronatum form 

 and characteristics until a late stage of growth. During old age the 

 whorl contracts as it does in Humphriesianum. The form and char- 

 acteristics of the young appear to indicate a derivation from some 

 coronatum form, like that found in the Parkinsoni-bed, Museum of 

 Stuttgart Collection. Another characteristic which seems to separate 

 it from the Goliatlius series is the general tendency of most of the 

 forms to become smooth on the abdomen, at a stage when Goliatlius 

 is furnished with prominent ribs. Notwithstanding these facts, how- 

 ever, whenever the adult forms come under observation, a similarity 

 becomes apparent which it is at present impossible to explain. 



The series which can be followed from Steph. contraction to Brocchii, 

 and its allied forms, is perhaps the most complete of all others, the 



1 With this compare the old coronatum described by D'Orbigny, referred to 

 above. 



