390 
SUPPLEMENT. 
Ascoceras stage, of a curious reversion to the Naufiloid stage (fig. 84, 
E). Erom this reversion of character ” Dr. Lindstrdm concludes 
that as the animal could hardly “twice modify its body,” there can 
have been but little (change in its structure in passing from the 
Nautiloid into the Ascoceras stage of its existence. 
Specimens are figured by Dr. Lindstrdm showing that the Ascoceras 
shell as a continuation of the Nautiloid shell was sometimes com- 
pleted without any septa. 
Dr. Lindstrdm considers that there can be no doubt that the shell 
of Ascoceras was external and enclosed the animal. The richly 
ornamented surface, the long body-chamber in the Nautiloid part, 
and the deposit of calcareous matter from within, after decollation, 
testify clearly to this fact. In the shell of Spirilla, which is only 
partially enclosed by the mantle of the animal, there is no external 
sculpture, nor is the uppermost chamber larger than the others, a 
living chamber not being re(}uired. Dr. Lindstrdm believes that an 
increase in the body of the animal in such genera as Gomphoceras 
and Poterioceras must have occurred ; he adds that the last named 
bears no slight resemblance to Ascoceras. He considers that the 
secretion of the sigmoid septa was begun after the shell had been 
completed, and the mollusc had drawn itself higher up in it. 
Thirteen new species of Ascoceras are described and figured by 
Dr. Lindstrdm, viz: — cochleatam, doliinn, Jistula, pupa, reticulatum, 
manuhi'ium, ampulla, collare, hujena, cucumis, decipiens, sipho, 
gradatum. 
The new genus Choanoceras ^ (fig. 84, G, II) is described as 
having a shell “resembling a faintly curved Orthoceratite, with the 
lower extremity truncated and conically pointed.” The aperture 
is probably simple ; the body -chamber very large, occupying almost 
nine-tenths of the whole shell. ' Septa from four to six, formed 
like a pointed, oblique funnel. All the septa are equally well 
developed in young specimens, but in the adult, in which there are 
six septa, three of these are complete, and the three earlier ones 
incomplete or lacunose. The siphuncle is nummuloid in the older 
individuals, cylindrical in the younger, and the necks of the septa 
hook-like and strongly recurved. This genus differs from Ascoceras 
in the slight development of its lacunose septa. The position of the 
latter appears also to be contrary to that of Ascoceras, sui^posing the 
convex side of the shell to be the ventral, and the concave the dor- 
sal, as is assumed to be the case in Ascoceras. In Choanoceras the 
^ From a funnel. 
