Hyatt.] 16 [January 17, 
widely gaping pile of the abdomen. This is the pervading charac- 
teristic of the growth of the individual throughout the series, and 
is as strongly marked in the young of Dactylioceras Braunianum as 
in any of the other species. The adult whorls of Dactylioceras com- 
mune are rounded, those of Holandrei flattened on the sides; in 
annulatum with sides flattened and tendency of the abdomen to rise, 
or become somewhat subangular; in Braunianum all these changes 
are consummated in a very flat form of the whorls, and a subangular 
abdomen. ‘The pile also cease to be divided on the abdomen in 
Dactyhioceras annulatum; and in Dactylioceras Braunianum the ab- 
dominal area is smooth. 
C@LOCERAS. 
Coceloceras pettos. 
Amm. pettos Quenstedt, Flotz., p, 178. ’ 
Amm. pettos Quenstedt, der Jura, p. 135, pl. 16, fig. 14. 
Amm. crenalus Zieten. Verst. Wurt., pl. 1, fig. 4. 
Amm. G'renouillouxit D’Orb., Terr. Jurass., Ceph., pl. 96. 
Celoceras pettos Hyatt, Bull. Mus. Comp. Zoology, no. v, p. 87. 
Celoceras Grenoullouzu Hyatt, Bull. Mus. Comp. Zoology, no. v, 
p: 94. 
In this species we find a remarkable form, flattened abdomino- 
dorsally; the sides very divergent, even in the adult, the abdomen 
rising with a gibbous curvature, and the involution reaching to the 
line of tubercles which ornament the outer edges of either side. 
These may be either mere folds vanishing at a short distance from 
the tubercles, or well defined pile, passing almost entirely across 
the sides. There is as slight change made in the septa by growth 
as in the shell. At the earliest period examined, about the third 
whorl, the sutures had the full adult proportions. The abdominal 
and superior lateral lobes were of about the same height, the inferior 
laterals very small, but the top is on a level with that of the superior 
laterals. The superior lateral cells are much longer than the in- 
ferior lateral; the latter, however, are remarkably broad and low. 
Whether the extreme young had lobes and cells, and an external 
form like Celoceras centaurus, I am not able to say, though they 
are similar to the adult of one variety of that species. The agree- 
ment of the name on several labels led me to quote Grenouillouxit 
independently, whereas it is evidently identical with Celoceras petios. 
