192 GENESIS OF THE ARIETIDA. 
the adult of Oor. Bucklandi of German authors. The pile are more widely sep- 
arated, about six less on the eighth whorl than on the seventh; they are thick, 
solid, untuberculated, and the geniculx 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 
genicule, 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 geniculx 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 pilz held 
their own wonderfully. There was also in the same Museum a specimen in which 
the pilze had genicule 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,” Bucklandi, Plate XI. Fig. 1,seems to belong to what we call true Buckland, 
as well as most of the figures of young on Plate X. The specimens figured as 
Amm. sinemuriensis, on Plate XI. Fig. 18-20, are doubtless the young of our Cor. 
Bueklandi, 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' is a form with much larger and fewer 
whorls than Bucklandi, 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 pile, 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. Their sutures, the huge fold-like, smooth - 
1 Wright, Lias. Amm., pl. i. fig. 1-3. 2 Amm. Schwiib. Jura, pl. viii. 
