492 Miscellaneous. 
examined. If in some of these the mantle enveloped the pedal 
region to a smaller extent, this seemed to me to be entirely due to 
the bad condition of the visceral mass, which, pressing upon the 
bottom of the sac, caused the whole to recede from the pallial 
investment. 
In the present note I pass over the sexual characters based upon 
the number, structure, and position of the tentacles, since it is my 
intention to deal with them shortly, and also because I would now 
insist only upon the characters that can be determined almost 
without the necessity of extracting the specimen from its shell. 
These variations in the shape of the last whorl of the shell in 
Nautilus macromphalus and N. pompilius naturally lead us to inquire 
whether these indications could not be utilized in paleontology. 
In the course of his investigations upon ammonites d’Orbigny put 
forward the theory, in 1841, that the variations in the size of the 
shell in these cephalopods, observed in the same species and among 
individuals of the same diameter, might be due to sexual differ- 
ences; in his opinion the more swollen shells should belong to 
females. 
This idea has been adopted by several naturalists, among whom t 
would mention especially P. Reynés. M. Douvillé likewise appears 
to entertain the same opinion. 
M. Munier-Chalmas, the learned professor of the Sorbonne, while 
admitting the sexual dimorphism of the ammonites, which he regards 
as dibranchiate cephalopods allied to Spirula, does not entirely 
adopt d’Orbigny’s point of view. To the differences in size he adds 
the presence in the males of jugal apophyses, which he considers to 
be wanting in the females. In an important note on “ the possi- 
bility of admitting a sexual dimorphism in the ammonites,” pub- 
lished in December 1892 in the ‘ Comptes rendus des séances de la 
Société géologique de France,’ he shows that groups of ammonites 
may be considered as the males of other groups which would be the 
females (thus Oecotraustes would be the male of Oppelia, Norman- 
nites the male of Cadomites, &c.). 
Without following this geologist into the study of the variations 
which he points out in a large number of types of Ammonitide, I 
would remark that, according to my observations upon ten specimens 
of Nautilus preserved in spirit, and also according to those made 
upon avery large number of shells belonging to the two most widely 
distributed species, Nautilus pompilius and N. macromphalus, the 
differences that are found to exist in the dimensions of the shell, 
although quite appreciable, are never very considerable, and that, as 
I have already stated, it is the shell of the male that, with an equal 
diameter, exhibits the larger size, contrary to that which, according 
to the geologists, is observed in the ammonites. 
It would be of some interest to pursue investigations of this kind 
in the group of fossil Nautilide, in order to see whether in the shells 
of these cephalopods there do not exist variations in size sufficiently 
