569 
reported as found at Colorado City Mineral Springs, and is in 
Museum of Comparative Zodélogy. 
Flelicoceras umbilicatum, Meek, Lnvertebrate Paleontology, Pl. 
xxii, Fig. 5, is probably a close ally of Stevensoni, but my informa- 
tion_is not satisfactory. 
Heteroceras Conrad, as figured by Whiteaves in Mesozoic Fossils, 
i, Pt. ii, Pl. xii, and supposed to be identical with Ammonoceratites 
Conradi of Morton is also a form that is not sufficiently well-known 
to be referred to its proper genus. The costz have no tubercles 
and resemble those of the young of WVostoceras Stantoni and helicinum. 
There is also obviously a retroversal gerontic volution shown by 
Whiteaves in his Fig. 3, and there is apparently no contact furrow, 
the mode of growth being helicoceran and not turrilitean. 
It may be useful in connection with these descriptions of phylo- 
gerontic forms to note the fact that there are some series of true 
ancyloceran forms in this country having shells revolving in sym- 
metrical spirals in the same plane, and not having helicoidal ephebic 
stages. They are similar to most of the European series, and it is 
not advisable to name them till proper comparisons can be made. 
Ancyloceras percostatum and Rémondi, Gabb, described in 
. Paleontology of California, are good examples of species having this 
kind of spiral. 
Lindigia. 
This genus Karstens,* with Lzndigza helicocerotdes as the type, has 
(in this small species) linear, untuberculated costz, a helicoceran 
spiral in the ephebic stage, and comparatively a very large and long 
retroversal gerontic volution. 
Heteroceras Conradi of Whiteaves may be a species of this genus 
occurring in North America, but Lindigia has peculiar ventral 
crests in the costee of the anagerontic substage that are quite dis- 
tinct from those figured by Whiteaves in his species. 
Felicoceras simplicostatum of Whitfield resembles this species, but 
it may nevertheless be the parephebic substage of some other tuber- 
culated species which has lost its ephebic tubercles. 
Nostoceras,+ n. g. 
The species of this genus have a close-coiled unsymmetrical shell 
during the ephebic stage and are true turrilites. There are two 
* Geol. de la Colombie, Venezuela, etc., Pl. i, 1856. 
+t Néorog, areturn. 
PROC. AMER. PHILOS. SOC. xxx1I. 148. 8 T. PRINTED JULY 24, 1894. 
