jgv; GENESIS OF THE AIUETID.E. 



the adult of Cor. BucMandi of German authors. The pilte are more widely sep- 

 arated about six less on the eighth whorl than on the seventh ; they are thick, 

 solid, untuberculated, and the genicular bend abruptly and squarely forward on a 

 level with or a trifle above the channel ridges, interrupting them with very slight 

 elevations. The abdomen is flattened, but more or less rounding between the 

 genicular, and its breadth is a trifle less than the dorsum, instead of being slightly 

 broader, as in the young during the first five or six volutions. The channels sink 

 into the abdomen, and the keel hardly shows above the lateral ridges. 



The sutures on the third quarter of the eighth whorl in this specimen have 

 an abdominal lobe about two fifths longer than the superior laterals, and the 

 inferior lateral saddles are also two fifths deeper than the superior laterals. 



A finely preserved specimen from Schaichhof agrees precisely in all its charac- 

 teristics with the above, but on the first quarter of the tenth volution the inferior 

 lateral saddles are about one third longer than the superior laterals. A specimen 

 from Semur on the latter part of the tenth volution had an abdominal lobe 

 about one third longer than the superior laterals. A slight rounding off of the 

 abdomen, greater prominence of the keel, and shallowing of the channels, indi- 

 cate the approach of old age in this specimen, whereas, at a corresponding age. 

 the Schaichhof specimen still had the angular genicular and flattened abdomen of 

 the adult. 



The largest specimen of the sinemuriense variety, as shown by the young, was 

 found in the Stuttgardt Museum. It measured about 610 mm. in diameter. There 

 were some indications of old age, but the form of the whorl and the pila? held 

 their own wonderfully. There was also in the same Museum a specimen in which 

 the pilae had geniculaB on a level with the abdomen, and therefore very promi- 

 nent, the channels excessively shallow, and keel broad and low ; it was 375 mm. 

 in diameter, and the channels had probably been deeper at earlier stages. 



Of the specimens figured by Quenstedt in his " Ammoniten des Schwiibischen 

 Jura," BucMandi, Plate XL Fig. 1, seems to belong to what we call true BucMandi, 

 as well as most of the figures of young on Plate X. The specimens figured as 

 Aram, sinemurienszs, on Plate XI. Fig. 18-20, are doubtless the young of our Cor. 

 BucMandi, var. sinemuriense. These forms are not rare, but the adults must be 

 rare, or they would not have escaped Quenstedt's attention. 



Var. Bucklandi. 



The stout English variety of Bucklandi 1 is a form with much larger and fewer 

 whorls than BucMandi, var. sinemuriense. The adult whorls are similar in their 

 general characteristics, but the young in the stout English variety has very 

 much larger whorls, with thick, sparse, single pilre, like the German specimen 

 in the Stuttgardt Museum described above and the young forms figured by 

 Quenstedt. 



The Amm. solarium of Quenstedt is founded upon large, senile specimens, as 

 is shown by the fragments figured. 2 Their sutures, the huge fold-like, smooth 

 1 Wright, Lias. Amm., pi. i. fig. 1 3 a Amm. Schwab. Jura, pi. viii. 



