FOURTH, OR CORONICERAN BRANCH. 181 



respect. A subsequent re-examination and remeasurement of all specimens in 

 the Museum of Comparative Zoology has shown that the average length of the 

 abdominal lobe for nealogic and adult shells is considerably over one third longer 

 than the superior laterals. The sutures also vary from the comparatively simple 

 margins, with solid looking and very slightly indented saddles, to the extreme 

 forms figured in our plates and by Quenstedt. 



Var. C. 



Plate IV. Fig. 9-11, 15, 16. 



In this variety the channels are slower in reaching their full development, and 

 the pilos are not so prominent, but are more numerous and conform more closely 

 to the shape of the whorl. The whorl is altogether flatter, and increases some- 

 what faster by growth than in variety B. The chaiinels are hardly perceptible 

 on the fourth volution, and in consequence of the smaller size and want of prom- 

 inence in the geniculae, the abdomen has at the same time more prominence than 

 in variety B. These characteristics are more or less variable. Thus individual 

 specimens may resemble variety A in some characters, or variety B in others. 

 In a specimen of variety C, Plate IV. Fig. '15, 16, senile characters begin to be 

 apparent upon the second quarter of the ninth whorl. The pihe are still slightly 

 tuberculated, the abdomen though much narrowed is still comparatively broad. 

 In a specimen of variety B, at same time the abdomen had become narrow, the 

 pilae had lost not only the tubercles, but also the geniculas, being in their second 

 stage of obsolescence. A specimen in the Museum of Stuttgardt, from Gop- 

 pingen, measuring 440 mm. in diameter, showed more pronounced senility. The 

 sides were exceedingly convergent, the pila3 obsolescing, the abdomen elevated, 

 though the channels and keel were not much changed. In another of the same 

 diameter the channels were obsolete, the keel a low broad ridge, the pilse reduced 

 to broad lateral folds, and the sides very convergent. In the large specimens 

 figured by Quenstedt, 1 if the figures are accurate, the keel, channels, and lateral 

 ridges are persistent. 



In the Museum at Semur is a fine suite of specimens named Vercingetorix, 

 Beynes. These specimens did not show senile decline as early as is usual in this 

 species. One at the diameter of 525 mm. still retained the pilse and the chan- 

 nels, though the abdomen had become much elevated. This specimen was dis- 

 torted by lateral pressure, so that the transverse dorsal diameter was shorter than 

 the abdominal. 



Wright's figure 2 seems to be identical with this species, and the more' com- 

 pressed specimen figured on Plate IV. seems to be intermediate between my Cor. 

 lyra and Cor. Gmnendense. I do not remember having seen any such forms myself, 

 nor are any English specimens mentioned in my notes. 



1 Amm. Schwab. Jura, pi. vii. 2 Lias Amra., pi. iii. 



