384 CRETACEOUS GASTROPODA 
is traceable about the middle of the whorls, having on the last whorl at the place 
where this one is deflected an elongated, kidney-shaped perforation surrounded 
by somewhat thickened margins; another small perforation is found about the 
centre of the basis, but in the outer lip, it is likewise surrounded with a raised _ 
margin. 
Prof. Suess very correctly compared the first perforation on the band with 
that of Trochotoma, or rather that of Ditremaria, as emended according to the 
last researches of Deslongchamps. The second perforation near the centre of 
the base is indeed very peculiar, and we have actually nothing analogous to it 
except the basal perforations of YZriphoris, and, as I believe, that of Hvelissa 
(see p. 189). M. de Ryckholt was evidently not acquainted with Prof. Suess’ 
detailed description of C. clathratum, when he stated that the genus is identical 
with Pleurotomaria (Journ. d. Conch., 1860, IV, p. 183). 
11. Ditremaria, d’Orb., 1843. Eug. Deslongchamps in a recent paper (Bull. 
Soc. Linn. Norm., 1865, IX, p. 427) again introduces d’Orbigny’s name for two 
well known jurassic species, D. globulus, Desl., and D. quinquecincta, Ziet., of 
both of which he had examined well preserved specimens. 
These shells somewhat resemble in the ovately conical form and the solid 
structure Catontostoma; the band has near the margin of the outer lip one long 
kidney-shaped perforation, being very much contracted in the middle; the centre 
of the base is provided with a strong callosity, which usually terminates at the 
inner lip with a prominent tooth. 
12. Trochotoma, Desl., 1841, has the base funnel-shaped, excavated, usually 
without a strong callosity; the band has one elongated perforation near the margin 
of the outer lip. In the paper quoted above Eug. Deslongchamps pointed out 
the distinctions which exist between this and the last uamed genus, the species 
of which are chiefly known from jurassic deposits. Specimens of intermediate 
growth often have a perforation and a short slit (see Bull. Soc. Linn. Norm., 1865, 
IX, pl. 3, fig. 4). 
13. Shismope, Jeffreys, 1856 (Ann. mag. nat. hist., p. 819—Woodwardia,* 
Crosse and Fisch., 1861, Journ. d. Conch., IX, p. 160), a name used for the recent 
species of Trochotoma, which agree in their small size with Scissurella, but differ 
from it by the presence of a single elongated perforation. A. Adams (Ann. mag. 
nat. hist., 1862, X, p. 846, ete.) described three recent species from the Japan 
and China seas, but he applies to them the name Scisswrella, and calls the typical 
forms of this genus, distinguished by a slit of the outer lip, Axatomus, Montt. 
I have already remarked that this last name of Montfort is inadmissible. 
Tt must be granted that these recent species do not, as regards form, differ 
from the fossil ones of Zrochotoma, but the former are said to have the internal 
layer of the shell not pearly, while the latter are supposed to be pearly within. 
Tf this be in reality the case, as suggested by Crosse (Journ. Conch., 1865, V, 
* This name has been formerly used by different authors and cannot be used again, even had it priority 
as compared with Shismope. 
