202 GENESIS OF THE ARIETID.E. 



depressed form of the whorl, and the coarse price which cross the abdomen have 

 a similar broad, flattened aspect. The siphonal saddle, according to Wright's 

 figures, Plate LXII. A, seems to have suffered considerable alteration from what 

 it is in the typical form of obtusum. The lobes and saddles of the Bempflingen 

 specimens have the regular differences of one half to one third in the lobes, and 

 the abdomen is unusually broad. 



There is a specimen of variety D, from Lyme Kegis, in which for a short 

 space the keel has been pressed inward and the sides ruptured. While on the 

 recovery from this injury the abdomen retained a flattened aspect, it is about as 

 broad as that of some forms of sagittarium, and otherwise similar. Narrow folds 

 and furrows are noticeable crossing the abdomen, which correspond to similar 

 small folds and furrows on the sides. The effect of the rupture is otherwise 

 noticeable in the temporary absence of the pilae and the greater intervals be- 

 tween the next two pairs of sutures. This example shows that there may be 

 a tendency to vary in the direction of Microceras, which is produced in some 

 specimens by disease, and in others by wounds. Such characteristics were not 

 observed in the later stages of diseased specimens. They probably disappeared 

 in course of growth, just as the similar characteristics of the young of Cor. 

 Sauzeanum were suppressed in the adult stages. 



The forms of this species may be divided into several varieties, according to 

 the adult characteristics, and the slower or quicker development of the keel, 

 channels, and form. 



Var. B. 



This has flattened sides, pilae not very prominent, but running nearly to the 

 base of the keel, and the channels are very narrow as well as shallow. 



Var. C. 



This is the normal Turned of Zieten, and has the pilae reaching nearly to the 

 base of the keel in the nealogic stages, and perhaps in the adult. In all other 

 characteristics, even in the prominence of the pilae, it agrees with variety D. 



Var. D. 



Plate IX. Fig. 1. 



This is the typical form, and has well rounded, gibbous sides, prominent pilae, 

 broad abdomen, broad shallow channels, and a depressed keel. 



Var. E. 



Plate VIII. Fig. 4 8. 



This is similar, but has deeper channels and a keel more prominent, narrower 

 and more convergent sides in the adult, showing some resemblance to Ast. 

 Turneri. Hauer's specimen of Amm. steUaris figured in " Nordostlichen Alpen" 

 belongs to this variety, and is not identical with the true del/are. 



The pilae may be gradually introduced by a series of plain folds, or by tuber- 

 cular folds, Plate VIII. Fig. 4, 5. The whorl is smooth in specimens having the 



