FOURTH, OR CORONICERAN BRANCH. 177 
more prominent. Upon either the latter part of the fourth, or first quarter of 
the fifth volution, the whorl attained its adult characteristics. 
During the first volution the increase laterally had been very great, forming 
a deep umbilicus; subsequently the tubercles and folds were added to the width 
of the abdomen of the earlier whorls, giving a general resemblance to Cor. datum. 
The young whorls of specimens in which the tubercles appeared later on the 
third whorl were usually rounder, and exhibited, when seen from the side, only a 
very remote resemblance to Cor. datum. These passed suddenly, so fast did the 
tubercles grow to be folds and then true pilx, into the stage in which they re- 
sembled Cor. kridion. After this stage, the preponderance of the abdominal 
region is not so marked, though it may be maintained throughout the fourth 
volution. Quenstedt’s young specimen, with a living chamber one volution in 
length,’ exhibited a broad abdomen on the fourth whorl. 
The genicule are at first not tuberculated, but sharp and angular, as in some 
varieties of Cor. kridion. The abdomen, however, does not usually become sufli- 
ciently prominent in the earlier stages of growth to bear comparison with that 
region in kridion. After this period the umbilical shoulders are developed more 
proportionally, and finally on the fifth volution the whorl becomes broader dor- 
sally than near the abdomen. The dorsal curves of the pile become more 
prominent, and sink or are contracted to form the tubercular genicule. These 
subsequently bend forward in some specimens, ascending the abdomen. This 
last character may occur earlier, on the third whorl, or, on the other hand, be 
omitted altogether, even in adults. 
This description of the stages of development may be curiously altered by a 
malformation of the abdomen. The pilw, Plate III. Fig. 7, 11,? are continued 
across, cutting up the abdomen into a series of waves entirely obliterating the 
keel and channels. 
This variety has young which differ considerably from one another in the 
relative breadth of the abdomen, some being excessively broad and flat during 
the young whorls, and others, especially the microceran forms, have much nar- 
rower whorls. The number of the pile also differs, these parts being more 
widely separated in the broad, flat young than in others. 
In the majority of adult specimens, the superior lateral saddles are deeply 
divided by two marginal lobes, and spread out laterally beyond, or on the ge- 
nicule. One specimen, however, from Semur, though not differing in other 
respects, has superior lateral saddles so long and narrow that the superior lateral 
lobes occupy the genicular line. The abdominal lobe extends beyond the supe- 
rior laterals by about one third, and the superior lateral saddles are of about 
the same depth as the inferior laterals, though much broader. 
Var. B. 
This variety is founded on two specimens, which maintained a broad ab- 
domen and the immature, thick, unshapely pile of the young until a late 
1 Figured in Amm. Schwab. Jura, pl. xv. fig. 9. 
2 Vig. 7 represents the abdomen erroneously, the forward donna of the pile where they meet on 
the abdomen being flattened out in the specimen. 
to 
we 
