TO i, \ 



i;i../.siX if we include in it, as we must provisionally do, all the Paleozoic 

 spirally striated shells which agree in other respects with nhon, may not be an 



entirely natural -jonus. I'.y this we mean that many of the later forms are probably not 

 .les.-en.le.l from the Trenton type of the genus. We think it possible that Bucanop- 

 >'.>- like species were evolved from ll?U,roj>h,m not only in Lower Silurian times but 

 at later periods as well. Again it is not unreasonable to suppose that certain 

 developmental lines, originating in some period preceding the Trenton, may have 

 resulted in forms that we cannot now separate satisfactorily from Bucanopsia. 



The last possibility is suggested by Koken's remarks on the development of the 

 shells which he erroneously places into Meek's genus Bucnnella (see this work pages 

 849, 876 and 882). If he is correct in regarding Bellerophon tubstriutus Krause, and 

 several I ifvonian >pecies mentioned by him, as having descended from his I/ower Silu- 

 rian l>. fxi/ionii. then the possibility is strengthened into probability; for B. esthona most 

 certainly came from quite a different stock than that which produced Bucanopsis 

 \ hile the supposed Devonian descendants are scarcely distinguishable from 



itopitis, and only by the slightly greater width of their slit-bands. However, we 

 are strongly inclined to doubt that Koken's views on the question under considera- 

 tion are ju-t Mi-->l \<y the facts. In our opinion, It. estliona,&$ well as a corresponding 

 American form, is quite distinct from most if not all of the others with which he 

 connects it, and it probably represents an undescribed genus with relations nearer 

 id Bucania than Bucanopsis* On a preceding page we propose the name 



nia for this new genus, and on plate LXIV figure the only known American 

 species of this type i A", costalis, page 882). 



B. militirinius Krause strikes us as a form that may have been developed from a 

 t twin like T. irisconsinensis. The characters known, it is true, are 

 insufficient to establish its affinities, yet if it could be proved that the inner whorls 

 retain only a trace of latero-dorsal ridges, we would overlook its somewhat different 

 >urfare markings and place the species with little or no hesitation under Tetranota. 

 Hut to show the difficulty of correctly estimating the generic affinities of many of 

 the bellerophonti'is from figures ami descriptions above, we may say that so far 

 nothing has been published of B. substring that might be considered as thoroughly 

 antagonistic to the view that would consider it as a modification of the Lower 

 Silurian Protoicarthin. in which delicate revolving lines are also often present. The 

 broad apertural sinus reminds one strongly of Protoirrfhin, and when it com- 

 the tripartite character of the shell, which character in connection with another 

 about to be considered led Koken to place these species with Bucnnflln, If. snlistr!<i(us 



to b* tU>ol tbmt kokrn rjr properly place* B. wttona In Uie InuMdlkta vIclDlly ul Uueaina or. u call It, 



