GASTROPODA. 931 
Raphistomid.] 
direction of the curve occurs is usually marked by a slight seam-like line 
or interruption. In Raphistomina and Huomphalopterus the sigmoid character 
of the curve is always distinguishable but there is no intermediate interruption. 
A true slit-band does not occur in any of the Raphistomide, yet it would be quite 
reasonable to consider the angular or lamellar periphery of the whorls as its 
representative. Or it may be that the slightly sinuate outer parts of the lines of 
growth on the upper side of the whorls are homologous with the lunulz crossing 
the band of true Pleurotomariide. Still, the evidence at hand is insufficient to establish 
either view. For the present then we have two well marked differences between 
the shells of the two families that may be utilized even should the suggested 
homologies admit of demonstration. The first of these differences lies in the 
absence of an apertural slit and the resulting slit-band, while the second 
may be expressed by saying that the retral sweep of the lines of growth in 
the Pleurotomartide is never diminished but, on the contrary, is nearly always 
increased just before reaching the band, while in the Raphistomide it is decreased 
and often overcome entirely on the peripheral carina. In cases like Hwomphalopterus 
alatus, in which the carina is extremely developed, the second curve is again 
overcome by a third which is strongly retral. The last, it seems to us, has no 
further significance than the preservation from injury of the anterior outer angle 
of the carina which would have been exceedingly liable to breakage if the second 
curve had continued. . 
We place here in all five genera. The position of the first three we regard as 
unquestionable, the fourth, Omospira, differs very decidedly from the rest in the 
rounded form of its volutions and relatively high spire, while the fifth, Scalites, is 
doubtful because there is yet much to learn respecting its most important charac- 
teristics. If the last should prove to have the really essential features of the family 
then its systematic position would most likely be between Raphistoma and Omospira. 
All of these genera have heretofore been placed with the Pleurotomariide. For general 
remarks on them, farther than those about to follow, the reader is referred to our 
discussion of that family on a subsequent page. 
Rapuistoma, Hall, 1847.* Shell sublenticular or plano-convex, the spire flat, 
the sutures close; volutions triangular in section, sharply angular and generally 
thin at the periphery; there is neither a slit nor a band; umbilicus varying in size 
but nearly always present; aperture turned backward slightly so as to form a 
shallow notch at the outer angle; lines of growth only; on the flattened upper surface 
these are slightly sigmoid and usually interrupted by a raised line between the two 
* Pal. New York, vol. i, p. 28, 
