502 
Mr. Stanton has kindly examined the numerous specimens in the 
National Museum, and estimates that the retroversal chamber in 
this variety is generally the sixth or seventh volution and also 
remarks that one specimen is nearly double the size of the largest 
one mentioned above, and that there are but few that are smaller. 
The three specimens I have of this variety are dextral, but there are 
others in the National Museum which are sinistral. 
Var. prematurum. 
This variety has more closely set costze and smaller tubercles and 
the gerontic stage begins earlier, there being, if my estimate is 
correct, only three or four closely coiled whorls. The last volution 
is well preserved in the only specimen of this variety that I have 
and this shows clearly an open aperture, almost straight across the 
venter, with slight crests on the sides and equally obscure crest on 
the dorsum. It is, in other words, precisely similar to the aperture 
of variety retrorsum. ‘The specimen here described is sinistral, and 
is the only one obviously belonging to this variety in the collection 
of the National Museum. 
Var. aberrans. 
This variety may have three, four or five closely coiled whorls 
and considerable variation in the tuberculations, etc., but when the 
gerontic stage begins, the aspect is distinct. The anagerontic 
substage does not bend so abruptly as in retrorsum or prematurum 
it is more oblique to the axis of the spire and the retroversal meta- 
gerontic substage, if it be superadded in this variety, would be more 
oblique than in var. frematurum. One specimen is dextral and the 
other is sinistral. 
Remarks. 
This species was discovered by Mr. Stanton in the Ripley beds, 
where it is associated, as stated by the same gentleman, with a 
number of other phylogerontic species, such as two species of 
Ptychoceras, Zurrilites splendens, Shum., Wostoceras (Turr.) hel- 
cinum, Shum., Helicoceras navarroensis, Shum., and a variety of 
other typical Ripley species. Mr. Stanton also informs me that out 
of 26 specimens in the National Museum, 16 are dextral and 10 are 
sinistral. 
