Hyatt. | 18 [January 17, 
vors the opinion that centaurus is a more or less degraded descendant — 
of Celoceras petios or of some common ancestor. 
Ceelcceras Desplacei. 
Amm. Desplacei D’Orb., Terr. Jurass., Ceph., p. 334, pl. 107. 
Celoceras Desplacei Hyatt, Bull. Mus. Comp. Zoology, no. 5, p. 94. 
The adults vary excessively, and the young also. They vary at 
all stages of growth, except the first few whorls which have sides 
invariably divergent. The sides may remain divergent with large 
spines, pile in knots, or may become flat or rounded, either with or 
without spines, or even flattened and convergent. Often without 
spines, the lateral pile single. The abdominal pile are always di- 
vided, but alternate with sixigle pile, which cross the abdomen with-. 
out interruption. Several specimens of this species, which were 
formerly referred in the Bulletin (No. v, p. 94) to Celoceras Grenou- 
dlouxii, exhibit the characteristics of the young very fully. These 
are extremely broad, with very divergent sides. The spines are 
large tubercles, each uniting a couple of pile, or only perhaps thick- 
ening one. These occur sparsely, and between them are entire pile 
which may either split on the abdomen into two or three, which is 
the more common way, or run across unbroken. This is also charac- 
teristic of the adult. The youngest stages, however, with their al- 
most smooth, highly divergent sides, and prominent tubercles on the 
edge of the abdomen gives very faithfully the prominent character- 
istics of the adult of Celoceras petios. 
In other varieties of Desplacei not only are the adults devoid of 
tubercles on the cast, but this may extend to the extreme young. 
Generally speaking, however, at some time during the life of an in- 
dividual, tubercles are present even on the casts. There may be some 
exceptions, but there are very few. When spines do not occur in 
the adults, as they do not, probably, on the shell itself sometimes, 
the sides are convergent, and they are conversely more prominent 
upon those shells which have divergent sides, like their own young, 
or the adult of pettos. 
Coeloceras a. 
This species is considerably smaller than Ce@loceras petios. The 
young are, however, very like the young of that species for a long 
period, then the sides become parallel and drop their tubercles, then 
convergent. The pile on the abdomen at this time cease to be di- 
vided, and sweep across the abdomen and sides as in the last variety 
of Celoceras Desplacei. During this period, also, the whorl de- 
