GASTROPODA. 993 
Liospira. | 
pages, are not amply sufficient for their separation and recognition? Raphistomina, 
as we have shown on pages 931-939, and 941, and as may be seen from the figures 
on plate LX VIII, has a very different aperture, being entirely without the peripheral 
notch and band. These differences are so important that the two genera cannot 
possibly belong even to the same family. As to our Trepospira, itresembles Liospira 
greatly, and may really be, though we are much inclined to doubt it, a lineal 
descendant of the Lower Silurian type. However that may prove to be, a generic 
separation must always be maintained because of the changing characters of the 
whorls of the spire and the short apertural slit which together characterize 
Trepospira and not Liospira. We refer the reader to page 957 for more detailed 
observations on these points. 
When it comes to Hotomaria, we are willing to admit something more than 
mere resemblance. The form in that genus is more conical than lenticular, the 
suture better defined, the lines of growth generally stronger, and the peripheral 
band situated entirely upon the upper side of the edge, while the inner lip, so far as 
known, is never reflected over the umbilicus as is so commonly the case in Liospira. 
In the latter the sutures are nearly always enamelled and so that part of the band 
is covered. In Hotomaria, on the other hand, all of the band is visible and the outer 
edge of the inner whorls projects slightly above and over the inner edge of the next. 
These differences, we believe, are quite sufficient to separate the two types of shells 
as distinct genera, especially as they hold their own without any appreciable 
tendency to run into each other. Still, we believe that one was derived from the other. 
Of the two genera Liospira probably was the older. We come to this conclusion 
because its band is of the convex type, which, it seems to us, is necessarily a more 
primitive structure than the concave band. The convex form of band we believe 
always points to an alliance with the Huomphalide which, theoretically at least, are 
older than the Plewrotomariide. Liospira undoubtedly began earlier than the Calci- 
ferous, in which it was represented by at least one good species. What it was 
derived from we cannot say at present, yet we feel convinced that Lophospira 
originated in the same stock. As to the origin of Hotomaria we are not so confident, 
still we are strongly inclined to regard it as evolved from Liospira. There is nothing 
unreasonable about this belief, for that the necessary changes in the position and 
character of the band may have occurred is indicated by L. decipiens, in which the 
periphery is sharp and that portion of the band which lies on its upper side is not 
‘only decidedly concave but much the greater part of the whole. 
We describe, and in most cases illustrate, a total of fourteen species of this 
genus. Besides these we regard Raphistoma previum Whitfield (Calciferous), Pleuro- 
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