E.\DOCEEATID^. 
131 
lapping of the posterior portion of the siphunciilar necks. The 
siphuncle is provided internally with a series of funnel-shaped sheaths, 
Fig. 13. 
Endoceras Wahlenbergi. — FragmeBt of the septate part of the shell in 
longitudinal section, showing s, s, septa ; sc, siphuncular cavity ; sh, sheatli ; 
en, endosiphon. From the Ordovician of Sweden. Natural size. 
E. belemnitiforme, and that “ in an example of E. Burchardii, Dowitz, the initial 
part was cigar-shaped as it is in the former species. The point itself was 
broken off up to a diameter of a few millim. ; but the septa were already 
developed.” Touching the generic significance of the initial chamber, he 
observes: — “Whether the construction of the initial chamber and the 
beginning of the siphuncle in the genus Endoceras agree with Endoceras belcm- 
nitiforme is unknown.” It appears to me, however, to be in the highest 
degree improbable that structural features of such importance as those just 
described should be peculiar to one or two species ; and I am strongly inclined 
to the opinion that we have here the typical structure of the genus. 
Dr. Holm states that only two examples of E. belemnitiforme are known to 
him. One comes from the upper red Orthoceren-Kalk of the Island of Oeland, 
Sweden, and the other from the Jaggowall water-fall in Esthonia, in the 
lowest beds of the Echinosphseriten-Kalk. These horizons correspond perfectly 
with each other. The species is also frequently found in boulders of the 
Orthoceren-Kalk at Heergermiihle, near Eberswalde, Prussia, where they have 
been collected by Professor Eeraele (Palseont. Abhandl. loc. cit. p. 9). 
The following considerations regarding the functions of the siphuncle, 
resulting from Dr. Holm’s studies of this most important and interesting 
species, are worthy of attention. He says that Zittel’s supposition that the 
siphuncle is best explained, according to the developmental history of the 
animal, as a remnant of the visceral sac, and that a fixed physiological 
function cannot be discovered for it, is not only rendered probable, but 
K 2 
