544 
bers of the same family when compared with the closely allied 
forms of the Triboloceratidz, all of which have a hollow central 
ventral zone at some stage. 
Lispoceras sulciferum, Fig. 24, shows the nepionic stage and 
ananeanic substage with form and characteristics approximately 
repeating those of Rineceras, and these resemblances are consider- 
ably closer than the figures would lead one to suppose. I did not 
notice until too late to replace them that these figures were not so 
complete as I had tlought them to be. 
The greatest development of the impressed zone in this family 
occurs in the compressed lenticular form of Phacoceras, Figs. 26, 
27, and although Fig. 27 is not entirely satisfactory in the young, 
as given by DeKoninck, it seems to demonstrate together with his 
description that the nepionic stage had a section which would place 
it either in this family or in some other with fluted whorls and a 
-gibbous abdomen. None of these genera have any species so far 
known which have a dorsal furrow, the impressed zone being 
strictly a contact furrow as in the Triboloceratidz. 
The genus Pselioceras of the Dyas is perhaps a member of this 
family, but I have strong doubts whether it does not belong to an 
independent family phylum in spite of the general similarity to other 
genera of Rineceratide. It is of some interest here because the 
umbilical perforation is very large, and it adds one more illustration 
to the many already noticed of shells having primitive forms and 
primitive modes of coiling in the young, which have the impressed. 
zone only in the shape of a contact furrow. ‘There is a slight con- 
tact furrow generated after the whorls touch in Pse/oceras cphioneum, 
sp. Waagen. 
Thrincoceras. 
I mention this genus of the Rineceratidz especially because I 
wish to correct here a curious mistake that has inadvertently oc- 
curred in my drawing of Zhrincoceras kentuckiense, p. 432, Fourth 
Annual Report of the Geological Survey of Texas. The section 
Fig. 13 shows a furrow on the free dorsum of the nepionic volution. 
A careful reéxamination shows that this does not exist. There is a 
mark due to erosion which occurs at the point previously examined, 
but this is not present on other parts of the same volution. 
The history of the impressed zone in this species does not differ 
from that of the same character in other genera of the same family 
