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bers of the same family when compared with the closely allied 

 forms of the Triboloceratidae, 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 thought 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 Triboloceratidae. 



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 Rineceratidas. 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 impress J 

 zone only in the shape of a contact furrow. There is a slight con- 

 tact furrow generated after the whorls touch in Pselioceras ophioneum, 

 sp. Waagen. 



Thrincoceras. 



I mention this genus of the Rineceratidse especially because I 

 wish to correct here a curious mistake that has inadvertently oc- 

 curred in my drawing of Thrincoceras 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 reexamination 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 



