GASTROPODA. 919 
Bellerophon similis.] 
Collections—Geological and Natural History Survey of Minnesota; W. H. Scofield; E. O. Ulrich; Dr. 
C. H. Robbins. 
Museum Register, Nos. 6765, 7399, 7449, 7463. 
BELLEROPHON SIMILIS, ”. Sp, 
PLATE LXTYV, FIGS. 31—39. 
_ This species is represented by about thirty casts of the interior and exterior, 
showing a decided constancy in its specific peculiarities. The form of the carinated 
volutions, indeed the general aspect of the whole shell in its usual state of 
preservation, is so much as in B. troosti that at first sight it may seem to be identical 
with that Kentucky and Tennessee species. A closer examination and better 
specimens, however, will soon prove them to be quite distinct. In the first place, 
the surface striations, instead of passing from each side almost straight across the 
back of the volutions to the carina, curve strongly backward, thereby forming a 
deep though wide-angled sinus in the outer lip. Next the strie are coarser, 
sublamellose, more regular and not arranged in bundles as in B. troosti. Further, 
the keel grows more prominent toward the aperture and the umbilicus is larger, 
though this is probably due entirely to the lesser thickness of the test. Finally, the 
aperture is of a different shape, less expanded laterally and less contracted by the 
callosity of the inner lip. The callosity is much less and forms no transverse ridge 
at the inner part of the lip. 
B. similis occupies an intermediate position between B. troosti and B. platystoma 
Meek and Worthen, the section of the volutions being as in the former, while all 
the other characters are more nearly like those of the latter. With ordinary care 
good specimens of B. similis and B. platystoma are not difficult to separate. B. similis 
has more rapidly enlarging and relatively fuller volutions, the dorsal part of the 
transverse section, if we exclude the carina, being almost semicircular, while in 
B, platystoma the slope on each side of the prominent keel is decidedly flattened. 
This difference in the transverse sections of the whorls we have found to be very 
reliable and of itself sufficient for the separation of the two forms excepting in a 
few cases in which the specimens were either poorly preserved or badly crushed. 
It remains to be mentioned that several specimens show very faintly a number 
of wide revolving bands. Whether these are structural or merely accidental has not 
been determined. Possibly they indicate color bands. 
Formation and locality.—Clitambonites and Fusispira beds of the Trenton group, Wykoff, Kenyon, 
and various localities in Goodhue county, Minnesota. 
Collections.—Geological and Natural Wistory Survey of Minnesota; E. O. Ulrich; W. H. Scofield. 
Museum Register, No. 8725. 
