196 
AUG. F. FOERSTE 
Hall. C. laterale and C. orodes are closely similar species. For 
these the term Amphicyrtoceras is proposed. Among other forms 
having about the same characteristics are Oncoceras futile Bil- 
lings, O. pettiti Billings and 0. teucer Billings. Streptoceras dif- 
fers from Amphicyrtoceras chiefly in the more triangular out- 
line of the aperture due to the anterior extension of the hypo- 
nomic sinus into a sort of lip. It probably was derived from the 
latter genus. Poterioceras is unknown in Silurian strata. 
Among gomphoceroid conchs, there is a primitive group, known 
to be represented in the Richmond and probably present also 
in earlier strata, which has only a moderate angulation at the 
hyponomic sinus instead of a strong constriction as in typical 
GompJioceras. For this group the term Diestoceras is proposed, 
with G. indianense as the genotype. This genus also includes 
G. obesum Billings and G. eos Hall and Whitfleld. 
Finally, the generic terms Westonoceras and Cyrtogomjoho- 
ce7^as are here proposed for the very aberrant species, Cyrtoceras 
manitobense Whiteaves and Oncoceras magnum Whiteaves. 
ACKNOWLEDGEMENTS 
It is needless to state that it would have been impossible to 
carry on the studies included in the present publication if it had 
not been for the good will and generous helpfulness shown by 
many individuals. I am especially indebted to Dr. R. S. Bassler 
of the U. S. National Museum ; Dr. E. M. Kindle of the Victoria 
Memorial Museum; Prof. Percy Raymond and Mr. Samuel Hen- 
shaw of Harvard University; Dr. Chester A. Reeds and Dr. E. 0. 
Hovey of the American Museum of Natural History ; Prof. J. E. 
Carman of Ohio State University ; Prof. Stuart Weller and Mr. 
Arthur W. Slocom of the University of Chicago; Mr. Henry L. 
Ward of the Public Museum of Milwaukee ; Prof. W. H. Shideler 
of Miami University; Mr. C. L. Faber of Cincinnati, and Judge 
Henry Pavey, now deceased, of Hillsboro, Ohio. Without as- 
sistance from these individuals, and the loan of specimens from 
collections under their care, little of permanent value could have 
been accomplished. 
I am under special obligations to Dr. David White and Mr. 
Walter C. Mendenhall, of the U. S. Geological Survey, for access 
to the facilities of that Survey, and for giving me every en- 
couragement. 
