138 PERMIAN FOSSILS. 
and separated. Crural base perforated. Foramen situated at the point of the umbone, 
and open inferiorly by the fissure." 
Type Atrypa pectinifera, J. de C. Sowerby. 
Cleiothyris, it will be seen by the above diagnosis, differs im several respects 
from Atrypa, the genus in which its type has hitherto been placed; and from dthyris, 
with which it is more closely allied, im having the dental plates immediately attached 
to the inner surface of the large valve, and in being without a medio-longitudinal plate 
in the opposite valve. Probably it also differs from <Athyris in the valves being 
generally furnished with variously-characterised projecting lamella of growth (as in 
Cleiothyris planosulcata, Phill., C. pectinifera, J. de C. Sow., and C. eapansa, Phill.) ; in 
the spirals being pectinated (vide Pl. X, fig. 10); and in having a perforate crural 
base’ (vide Pl. X, figs. 8,9). Looking at the figure which Mr. T. Davidson has 
published of the spiral apophysary system of the small valve of a species apparently 
belonging to Athyris,’ there appears to be a wide difference between this genus and 
Clevothyris in their respective spiral crura, which, in the latter, are similar to those of 
Trigonotreta; whereas, in the former, they appear to be conjoined for a considerable 
extent, so as to resemble a long wire-like process, forked at its termination, near the 
centre of the shell, each fork appearing as if it passed into, or became connected with, 
the spiral to which it is directed. 
The projecting lamelle of growth are evidently the same as those characterising 
certain Discinas. The minute punctures noticed in the diagnosis are displayed in 
some of my specimens of Cleiothyris ambigua (Spirifer id., J. Sow.) Respecting the 
use of the perforation in the crural base, Iam unable to offer any opinion. Has it any 
relation to the wire-like process above noticed ? 
I am not aware of the occurrence of species of this genus in any other than 
deposits belonging to the Carboniferous and Permian systems. 
CLEIOTHYRIS PECTINIFERA, J. de C. Sowerby. Plate X, figs. 1-10. 
“ SPHEROIDAL”’ TEREBRATULA, J. de C. Sowerby. Trans. Geol. Soc., 2d series, vol. iii, 
p. 119, 1829. 
ATRYPA PECTINIFERA S Min. Conch., yol. vii, p. 14, pl. 616, 
(all the figures,) 1841. 
be used in such a sense: further, as a group of shells hitherto placed in Atrypa requires a name, I have 
made free to adopt Professor Phillips’s rather than propose one myself, a step which has one recommendation 
in its favour, that of using up a synonym. ; 
1 The following is the diagnosis given by Professor Phillips: ‘‘ Cardinal area obsolete, beak incurved 
over a minute perforation, which is often obtect, or merely serves to receive the beak of the smaller valve.” 
(Paleozoic Fossils, p. 55.) 
2 Cleiothyris ambigua (Spirifer id., J. Sow.) has a perforated crural base. 
3 Vide Bull. dela Soc. Geol. de France, 2™° série, t. v, pl. iii, fig. 26. 
