GASTROPODA. 885 
Bucania.] 
Concerning the slit, perhaps not one specimen in a thousand of the B. sulcatina 
section preserves it entirely. Asa rule the delicate apertural portion of the shell is 
broken away quite to the posterior end of the slit. In the other section a complete 
aperture is a much more frequent occurrence, both because the slit is shorter and 
the shell stronger. 
It will be noticed that the characters brought out in the foregoing paragraphs 
are different from those pertaining to much the greater part of the genus as defined 
by Waagen and Koken. They derived their ideas of the genus chiefly from Upper 
Silurian, Devonian and Carboniferous spirally ribbed species, which with few 
exceptions (none of them true Bucania) will fall into the genus that we propose to 
call Bucanopsis. It is to be noted, however, that Koken with his usual acumen 
draws attention (op. cit., p. 380) to differences in the aperture and surface sculpture 
between the “Swlcatina-typus” and the Devonian and Carboniferous species. 
Unfortunately he did not, or for want of material could not, carry his comparisons 
to their logical conclusion. 
According to our opinion Bucania, as here restricted, is (1) strictly a Silurian 
genus and possibly not even represented in the Upper. Silurian, (2) it is the stock 
from which Salpingostoma, and later Tremanotus, was derived, and (8) it is not 
genetically related to Bucanopsis. In support of the first statement we have the 
fact that while the twenty known Lower Silurian species fit closely together, not 
one of the succeeding forms could be included without materially altering the 
generic diagnosis. The truth of the second statement is but too apparent to those 
- who are obliged to discriminate between imperfect specimens of associated species 
of Salpingostoma and Bucania. Casts of the former from which the abruptly 
expanded aperture has been broken away, and on which the dorsal fissure is not 
clearly represented, are most difficult, if indeed it is at all possible, to separate from 
casts of Bucania. The important agreement, however, lies in the surface sculpture 
which in all essential respects is the same in the two genera. But it is scarcely 
necessary to discuss the relation of Bucania to Salpingostoma here since we shall do 
so quite fully some pages hence in our remarks on that genus. The third statement 
refers to Bucanopsis. This genus was evolved, we think, not from Bucania but from 
Bellerophon. No better description of the genus could be given than that which says 
that it includes species agreeing in all respects with Bellerophon excepting that they 
have revolving striz which, with the transverse lines, produce a cancellated sculpture. 
Without the revolving lines Bucanopsis would be nothing more or less than Bellerophon. 
Not so, however, with Bucania, since that genus would still be distinguishable. 
Again the spiral lines are not the same in Bucania and Bucanopsis, being straight 
in the latter and not oblique nor wrinkled nor ever interrupted as in the former. 
