12 G. LINDSTRÖM, THE ASCOCERATIDA AND THE LITUITIDA. 
Family ASCOCERATIDE. 
This family comprises as far as at present is known four genera, viz: 
Ascoceras BARR. 
Glossoceras BARR. 
Billingsites HYATT. 
Choanoceras n. g. 
The common feature in their structure, that unites all these genera, is the abnormal 
growth and morphology of the septa formed during the last stage of their existence. Having 
begun with regularly formed septa the later ones are bent obliquely in a sort af a high 
saddle towards one of the sides, and all that succeed the first sigmoid septum are incomplete 
or leave a large lacuna in their central part, which lacuna is framed by the lateral bor- 
ders of the septa. The siphuncle is broad, with nummuloid or bulbous elements. The 
three first genera have attamed a more pronounced development of the characteristic struc- 
ture, which has been coming on by degrees in Choamoceras, without such a sudden trans- 
ition from a Nautiloid stage as in them. A common feature for them all is the trunca- 
tion which seems to have been repeated several times. 
The systematic position and the affinities of this family have long been a puzzle, 
at least as long as the last stage of growth was the only one known. As BARRANDE left 
this group, it consisted of the two genera Ascoceras and Glossoceras, he himself having 
declared that Aphragmites could not any longer be retained as a genus of its own and 
that its both species coincided with true Ascoceras forms. BARRANDE regarded this fa- 
mily as of equal significance as the large families of the Nautilidx and ofthe Goniatitide 
and gave it a collateral place, as the third family of the Bohemian Cephalopoda. He has 
been in this respect followed by FiscnER in his recent »Manuel de Conchyliologie». But 
nearly all the other authors, who more or less extensively have mentioned these fossils in 
their memoirs or Manuals, have placed the Ascoceratida in immediate vicinity of Gompho- 
ceras. So BILLInGs, GIEBEL, WILTSHIRE, WRIGHT, BLAKE, ZITTEL and Foorbp. This has 
in some respect been caused by the accidental similarity of the truncation and in some 
degree by the inflated shell in these genera, which also seems to have lead some authors to 
accept the idea that Ascoceras and still more Aphragmites was in its entirety the living 
chamber of the animal. FERD. ROEMER places Ascoceras next to Trochoceras, BRONN and 
WOODWARD next to Gyroceras, PuruiepPr between Lituites and Cyrtoceras. NICHOLSON in- 
cludes it within his family of the Orthoceratidee. 
