GASTROPODA. 937 
Raphistomida.] 
being thickened at the outer and inner corners. This agrees with Ophileta, as does 
also the form of the aperture, and the course of the lines of growth. Finally, the 
position and character of the “collar” is certainly much more like the notch-keel of 
Ophileta than the more obtuse keel or angulation which marks the position of the 
rather broad and more shallow upper sinus in Kecyliomphalus. 
Loosely coiled or disconnected whorls we do not consider as an essential 
characteristic of Hecyliopterus. All the species may perhaps exhibit a proneness to 
assume such a condition but it is certainly not very apparent in any of the American 
species. Of the latter, . volutatus Whitfield sp., (see plate LX XIV) is the only one 
known to us having all the whorls separate, and it is doubtless closely related to the 
Kuropean LH. alatus Roemer sp., the type of the genus. Then we have LH. triangulus Whit- 
field sp., also from the Calciferous at Providence island and Fort Cassin, Vermont, 
which is exceedingly like the Swedish H. replicata Lindstrém sp., especially when it has 
the inner whorls in contact. The next species, our E. beloitensis, is from the Stones 
River group. It, like the preceding, hasa representative in Europe, being apparently 
very similar to H. marginalis Hichwald sp. All the whorls are in contact in this 
species excepting occasionally the apertural portion in old examples. The fourth 
American species is the Ophileta ottawaensis of Billings, from the Trenton of Canada, 
while the fifth and, so far as known, the last is the Ophileta owenana of Meek and 
Worthen, casts of which are not uncommon in the Trenton group of Minnesota and 
Illinois. In both the whorls are always in contact. From the foregoing statements 
it is evident that, in the development of the genus from the Calciferous on, the 
evolute or free character of the whorls became gradually less and finally was lost 
entirely. All the other characters, however, are maintained with rare persistency. 
If Eecyliopterus and Raphistoma are sections of the same line of development, 
then the evidence of their geological distribution indicates the former as the parent 
stock and not the latter, since Raphistoma occurs so far as known first in the Chazy 
when Hecyliopterus, which enjoyed its greatest development in the Calciferous 
formation, had already begun its decline. We do not wish to deny that much may 
be said in favor of such a derivation of Raphistoma, still we are confident that the 
modifications required are more difficult to prove and altogether less rational than 
in the view which derives the genus from Raphistomina. Billings has described a 
number of low-spired Calciferous and Quebec species among which we expect to 
find links connecting the last genus with the Chazy Raphistoma. His Pleurotomaria 
hortensia and Pl. harpya promise the required conditions. 
In Raphistoma the spire of the upper side varies from flat to gently convex, but 
so far as we have observed, it is never sunken; the keel forms the periphery and is 
directed outward instead of upward; the umbilicus is always smaller, and the section 
