366 CRETACEOUS GASTROPODA. 
22. I may mention here that the subconical or pyramidal fossil species the 
shells of which consist of numerous, plane and smooth whorls, like the cretaceous 
Trochus frumentum, Pict. et Camp., and probably Zr. Astierianus, d’Orb., or the 
jurassic Troch. epulus and Acteon of d’Orb., have to be distinguished as a separate 
genus. 
23. The umbilicated, many whorled, spirally striated or smooth species, like 
the jurassic Tr. late-wmbilicatus, Tr. Marie, Tr. Cirrus of @Orbigny, Tr. lautus, 
Stol. and others, ought most likely also to form a distinct genus, while the allied 
species with a convex basis and square aperture appear more nearly related to Miso. 
There is a great want of any critical examination of all the varied forms of 
jurassic TRocH1D#. 
24. Turcica, H. and A. Adams, 1854 (Gen. I, p. 423). Shell rather thin, sub- 
conical, with solid columella, twisted posteriorly, inner lip with one or two fold-like 
teeth. H.and A. Adams only mention the Australian 7. monilifera, A. Adams, 
being the type of the genus, but I rather think that there have been some addi- 
tional species described since. 
The only known fossil species which most probably belong to this genus are 
Trochus* Guyotianus, Tollotianus and Nicoletianus, described by Pictet and Roux 
from the “Grés verts” of the neighbourhood of Geneva (Moll. foss. 1847-1853, 
pp- 202-204, pl. 19, figs. 8, 9, and 10). The last of these is doubtful, being only 
known from a cast, having the whorls rather roundish, and thus resembling Troch. 
dentigerus, d’Orb., which more likely belongs to Huchelus. 
24a. (Trochodon), Seeley, 1861 (Ann. mag. nat. hist., VII, p. 289), not ¢dem, 
Agass. pro Trochidon, Swains. This was proposed for a species, Ty. cancellatus, 
from the Cambridge Greensand. The shell resembles a Zziphinus, is said to be 
thin, having on the columella two prominent teeth; it is therefore much more 
likely that it is generically not different from Turcica. 
24b. Ptychostylis, Gabb, 1865 (Proc. Calif. Akad., III, p. 187), according to 
the characteristics given by Gabb, apparently does not differ from Turcica. The 
columella is solid with two oblique folds; P. caffea from California is quoted as the 
type. 
25. Thalotia, Gray, 1847 (H. and A. Adams, Gen. I, p. 420). The columella 
is in this genus solid, anteriorly twisted, tuberculated or spirally grooved, the 
aperture anteriorly sub-effuse. The conical shells are generally rather solid, with 
the outer lip internally somewhat thickened, the more depressed ones thinner 
and with the lip simply furrowed, but not markedly thickened. Recent species 
of Thalotia are said chiefly to occur in the Australian seas; one rather globose 
species was lately collected on the Ceylon coast by Mr. G. Nevill. 
There are several species known from tertiary deposits, but I am not acquainted with any 
well preserved specimens from the cretaceous and from the jurassic rocks. I could only mention 
species like Turbo Buvigniert and globatus, d’?Orb,, which most nearly approach to it. 
* Some other allied forms like Turbo Golezianus and Sazoneti, Pict. and Roux (Moll. Grés verts, pl. 19, 
figs. 14-15), Turbo Dujardini, Coquand (Const, pl. 2, fig, 8), and others appear to belong to Amberleya (p. 262), 
of the LITTORINID#, 
