66 | CRETACEOUS GASTROPODA 
result of the examination of the two oldest species of Oniscia and Cythara, I may 
therefore record, that while both of them show very remarkable affinities in the 
general growth of the shell to each other, each of them separately retains still the 
typical characters of its respective family. Unless, therefore, it could be proved by 
anatomical researches on the animal of Cythara, that it has very little in 
common with the organization of the Pzzvrorourp (apparently a very improbable 
case) and that it agrees much more with that of the other Casszprpm™, Gray’s proposed 
classification of this genus in the latter family cannot be accepted. 
One point may be worthy of notice. Gray quotes among his distinctions 
between Oniscia and Morwn, that the outer lip of the former is reflected and 
rounded (in front !), while in the latter it has a shelving outeredge. The outer lip of 
Cythara has also a shelving outer edge, while in the cretaceous species, which we 
describe, the outer lip is reflected, rounded in front, and with a blunt, broad outer 
edge. It would appear, therefore, that there exists a similar difference between the 
Cyth. cretacea and the living species of Cythara, as between Oniscia and Morum 
of Gray; but I have already stated, that this difference between Oniscia and Iorwm 
appears to me to be so much subject to variations during the age of even one and the 
same species, and depending so much upon the localities and modes of life of the 
species, that I do not think it can be fairly used as a generic distinction. The fact 
is, however, worthy of record, and it is possible that some further enquiries may 
prove to be in favour of this reported distinction, as our knowledge daily advances. 
It is difficult to say anything about the fossil species of Cythara, although they 
are not wanting either in the neogene or eocene deposits; they are all described 
under Plewrotoma or Mangelia. A similar remark applies to the cretaceous species, 
although, if the Pl. arata, Gabb (Proc. nat. sc. Phil. for 1860, p. 198, Pl. 3, 
Fig. 9) does not belong to this group, I am not aware of any other, which would 
bear approximately the characters of the genus. 
1. CyYTHARA CRETACEA, Stoliczka. Pl. V., Fig. 10. 
Cyth. testa elongate-ovata, spira brevi, acuminata, anfractibus subconvexis, 
4.5, striis spiralibus atque costulis transversalibus cancellatis, ultimo spira multo 
longiore; canali brevi, vix curvato, antice late emarginato; apertura ovali, antice 
atque postice subacuta; labio calloso, ultimum anfractum infra partim tegente, ad 
marginem internum papillose crenato; labro parum extenso, ad peripheriam in- 
crassato, prope terminationem posteriorem late msinuato, intus anticeque undulate 
dentato. 
Width of the last whorl : total height of shell (considered as 1:00) oo (OWES 
Height of aperture : ditto ditto aq «0°69 
An elongated ovate shell, convex above and somewhat flattened below, the 
last whorl enveloping the previous to a great extent and occupying somewhat more 
than two-thirds of the total height. The convexity of the whorls is not consider- 
able, and their surface is cancellated by spiral striz and transversal ribbings. The 
