-TKOl'OKA '.'!'. 



f..ptKH> .In, III. I 



CMbeffeM. Geological and Natural Id-tor - >t.i. \\ II. Scofleld; E. O. t'lrirh; l>r. 



* ll. 



Mtueum Remitter, New. 76&, 7390, 7440, 743. 



HKLLKKOPHON HIMILIS, . p 







1 1 ATE LXIV. FIOB. n-m. 



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 murli ;is in If. troosti that at first sight it may peem to be identical 

 witli 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 striae 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 specimen- of H.ximilis and li. pl<ily.ttoma 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 

 /.'. }>l'ity.it<nn 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 ban<U. Whether these are structural or merely accidental has not 

 been determined. Possibly they indicate color bands. 



Formation and tocaHtg. CHUtuboniten and FusUpira beds of th.-Tn-nton group, Wykoff. K. 

 tod various localities ID Goodhue county, Minnesota. 



OoUectimu. -Geological and Natural History Surv.-y ,f Minn.-., , I O, 1'lrlch; \V II - . Held. 

 Regifter. No. 8725. 



