KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 23. N:o |2. 19 
most of these is the truncated extremity. A comparison with such forms as Ascoc. fistula 
(pl. 1 f. 20, 22, 24, 25) where there also are two regular septa beneath the first sigmoid 
one, a peculiarity which is restricted to a certain group of Ascoceras, makes it evident 
that Asc. Murchisoni BARR. also had two such regular septa and that none of its deciduous 
Nautiloid ones has as yet been found. The Ascoceras begins where the truncated septum is 
situated and has been augmented from within by thick deposits. Or rather, it begins 
with those septa which have a bullate or nummuloid siphuncle, as these have, but it ne- 
ver begins with the first sigmoid as Asc. Murchisoni should have done according to BAR- 
RANDE and Foorp. Neither BARRANDE nor any body of his followers had consequently ever 
seen the »partie caduque», as Foorp supposes"). Nevertheless BARRANDE had adopted the 
views of BROoNN that the shell through decollation had lost a certain number of air chambers, 
but he thinks that they could not have been many in the series and probably only one. In 
the last notice, however, he thinks that the series of deciduous septa was considerably 
elongated and that truncation occurred several times. 
BARRANDE'S immediate followers, GIEBEL, PHILLIPPI, FERD. ROEMER and SALTER ad- 
ded a little to our knowledge of the geological distribution of Ascoceras. BILLInGs (Ca- 
nad. Rep. for 1853—56 p. 310 and in subsequent papers) described three new species and 
as he had only mnuclei to study, he saw the continuous outlines or sutures of the septa 
across the shell and he also says of the siphuncle that it is situated »one line» from the 
»dorsal» (= ventral) side and is very narrow. 
BLAKE in his British Fossil Cephalopoda says that the sigmoid septa are parts only 
of those on the opposite side (the ventral). But again he talks of »hidden» septa and 
»sigmoid» septa, as if there were two different sets, and means with the former the 
ventral portion of the sigmoid ones. The sigmoid portions of the septa do not coalesce 
into a single septum, as he thinks, but, as shown above, they are distinct and separate, 
lying above each other, as seen by the sutures, though incomplete in their midst and 
meeting a little inside. When he says that the sigmoid portions of the septa not are 
developed in Aphragmites, it might be inferred that he supposes that the other portions 
were developed, but in that assumed genus no septa at all are to be seen, excepting the 
oldest Nautilidean one. Why they should be called »hidden» in Ascoceras I cannot find, 
as they are plainly visible on the ventral side of well preserved nuclei and by no means 
constantly hidden. He says that, the earlier part is unknown and still he further on 
states that the earlier septa are of the ordinary kind. 
HraATtTtT (Genera of fossil Cephalopods, Proc. Bost. Soc. N. Hist. XXI, April 1883 
p-. 279) gives some short notes concerning this and kindred genera. His systematic views 
of these have been mentioned above. It is somewhat startling to find that he describes Bil- 
lingsites (p. 278, probably the same genus as named Billingoceras on p. 279) as having septa 
continuous with the septa on the dorsal side and then again speaks of the »imperfect septa» 
of Aphragmites. His opinion that the sigmoid part of the septa is to be regarded 
as »large dorsal saddles»> is probably well founded. Of Aphragmites he says that BARrR- 
RANDE originally made it with »simple septa and sutures», but on consulting the work 
of BARRANDE it is evident that he described it as deficient of septa and consequently 
1) Geol. Magazine, 1889, p. 121, Note on the deciduous septa of Ascoceras Murchisoni. 
