GASTROPODA. 923 
Bucanopsis.] 
Bucanopsis, if we include in it, as we must provisionally do, all the Paleozoic 
spirally striated shells which agree in other respects with Bellerophon, may not be an 
entirely natural genus. By this we mean that many ofthelater forms are probably not 
descended from the Trenton type of the genus. We think it possible that Bucanop- 
sis-like species were evolved from Bellerophon 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 Bucanopsis. 
The last possibility is suggested by Koken’s remarks on the development of the 
shells which he erroneously places into Meek’s genus Bucanella (see this work pages 
849, 876 and 882). If he is correct in regarding Bellerophon substriatus Krause, and 
several ]Jevonian species mentioned by him, as having descended from his Lower Silu- 
rian B, esthona, then the possibility is strengthened into probability; for B. esthona most 
certainly came from quite a different stock than that which produced Bucanopsis 
carinifera, while the supposed Devonian descendants are scarcely distinguishable from 
Bucanopsis, 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 justified by the facts. In our opinion, B. esthona, as 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 
Tetranota and Bucania than Bucanopsis.* On a preceding page we propose the name 
Kokenia for this new genus, and on plate LXIV figure the only known American 
species of this type (K. costalis, page 882). 
B. substriatus Krause strikes us as a form that may have been developed from a 
species of Tetranota like T. wisconsinensis. 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 
surface markings and place the species with little or no hesitation under Tetranota. 
But to show the difficulty of correctly estimating the generic affinities of many of 
the bellerophontids from figures and descriptions above, we may say that so far 
nothing has been published of B. swbstriata that might be considered as thoroughly 
antagonistic to the view that would consider it as a modification of the Lower 
Silurian Protowarthia, in which delicate revolving lines are also often present. The 
broad apertural sinus reminds one strongly of Protowarthia, and when it comes to 
the tripartite character of the shell, which character in connection with another 
about to be considered led Koken to place these species with Bucanella, B. substriatus 
*Tt is to be mentioned that Koken very properly places B, esthona in the immediate vicinity of Bucania or, as we call it, 
Tetranota bidorsata,. 
