510 
asserts that lines of growth in Lituites and Ancistroceras are similar 
and certainly this appears to be in part true. ‘There are distinct 
inflections indicating the probable presence of five crests and five 
sinuses as this author states. These are perfectly well shown in Amc. 
Torelli, as figured by Remelé, and in his Ane. (Stromb.) Bolt. 
But in all of these there are other characters not found in Lituites 
or in other genera of this family which separate these fossils as a 
distinct group in my opinion of generic value. 
While the lines of growth are similar, they show that differences 
must have existed in the form of the crests and sinuses on the dorsal 
side of the aperture corresponding to the slight development of the 
median minor crest and paired minor sinuses on the dorsal side. 
In fact when one describes the curves of the dorsal lines of growth 
as indicating a dorsal crest in place of a lobe, he is coming nearer 
to the actual aspect than when he correctly classifies the outlines as 
a broad sinus subdivided by a minor crest and secondary sinuses. 
In other words, the great dorsal sinus of Lituites has reached the 
disappearance point in this genus during the ephebic stage but has 
not entirely vanished except perhaps in some species. It, also, as. 
is well.known, is a much larger, broader form, spreading out rapidly 
in the outstretched or free part of the whorl. It is also plain that 
the enrolled part or young shell of Ancistroceras has fewer and less. 
closely coiled whorls than in Lituites. Thus 4. Zored/, as figured 
by Remelé, has only one to one-half volutions enrolled and these 
do not touch although closely approximate. In fact the young of 
Ancistroceras are only coiled during the nepionic stage, and perhaps 
ananeanic substage, and the figures show much larger, stouter whorls. 
even at the apex than in Lituites. The figures of Remelé of 
A. Torelli and of Notling of 4. wndulatum are very careful studies, 
and exhibit the changes in development of the lines and annuli. 
These have in the neanic stage subacute, narrow crests, lateral 
sinuses rising to prominent ventro-lateral: crests and between these 
on the venter is a deep, broad median sinus, thus resembling those 
of Cyclolituites. The paraneanic substage is present on the early 
part of the outstretched whorl in Zore//i and undulatum. 
The siphuncle is also much larger in this genus than in Lituites. 
The study of the pseudo-septa by Holm led him to observe the 
siphuncle in 4. wudulatum and Torelli and his description is as 
follows :* ‘* Der siphonen scheint mir wenigstens auf der einen oder 
* Paleontol. Abh., Dames u. Kayser, iii, hft. i, “ Organiz. Silur. Ceph.,’’ 1885, Pl. xxi. 
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