180 CRETACEOUS GASTROPODA 
angular, and so far as can be seen from the direction of the strize very slightly 
produced in front. There is a true umbilicus present, and the inner lip is reduced 
to a small posterior portion attached to the previous volution and provided with a 
single fold. Such great differences as these in the formation of the shell certainly 
necessitate the proposition of a new genus, as has been done by Pictet and Cam- 
piche; the authors equally express their opinion as to the relation of this genus 
with Nerinee. 
The present known species of Cryptoplocus are the following :— 
Jurassic. 
C. depressus, Voltz. (Bronns’ Jahrb. 1836, p. 549, Pl. VI, Fig. 17), Peters, in his able paper on 
the Nerinee of the upper Jura (Sitzungsh. Akad. Wien, 1855, vol. XVI, p. 862), draws attention 
to the discrepancy between Bronns’ figure and description, and that of D’Orbigny, described 
under the same name and figure (Pl. 259) as Ner. wmbilicata (? Voltz.) D’Orbigny. If we had to 
judge from mere figures, certainly the convexity of the whorls in the latter and the difference in 
form and position of the fold would indicate another species, which could remain, 
1a, under the name Cryp. wmbilicatus, although it would not be very characteristic. I do 
not think, however, that Bronn’s figure is quite so safe as to guarantee this alteration. All these 
shells, as I have already noticed, erode very much even during life-time, and convex as well as 
concave whorls of Nerinee appear often as quite flat. ; 
1 4. Zieten figures (Petrf. Wurtbg. 1830, p. 48, Pl. XXXVI, Fig. 8) a species from the coral- 
rag of Nattheim as Nerinea terebra. It is evidently a true Cryptoplocus allied in form, but much 
thinner than any known specimens of C. depressus; the whorls are slightly concave, and the sutural 
angle about 16 degrees. 
1c. Goldfuss (Petref. Germ. III, p. 40, Pl. 175, Fig. 7) figures another very similar form, 
as N. subpyramidatis, Mist, which agrees very much with the original V. depressa of Voltz. The 
Nerin. depressa, Voltz of Zeuschner (in Haidinger’s Abhandlg. 1850, II, p. 137, Pl. XVI) could 
probably be added to this series, but it differs markedly from the others by its sutural swellings. 
Quenstedt (Jura p. 765) is of opinion that most of these forms are identical, and he may be 
correct in this. For comparison only I had taken the proportions of the height to the diametral 
width of one whorl in the different forms, which had been figured, and they arrange themselves 
thus— 
Ner. terebra in Zieten p08 .. height : width (consd. as 1:00) = 0:47 
,, depressa of Bronn vie me of 4 Bf 0:59) 
Bs » Of Zeuschner, Fig. 2 ... es 4 6 = 0:38 
55 s a 1s dh Go5 op a5 a = 0°35 
» umbilicata, in D’Orbigny i Bs By a = 0°35 
» subpyramidalis in Goldfuss ... Ee a a) = 0:34 
With respect to these measurements we could justly separate at least two forms, the Cryp. 
éerebra, Schiibl. sp. and the other four under the name of Cryp. depressa, Voltz. sp., but as other- 
wise no well preserved specimens of all these forms, which have been referred to, are as yet known, 
or have not at least been examined, it would perhaps not be advisable to fix these specific alter- 
ations at present. 
2. Cryptoplocus pyramidalis, Miinst, sp. (Nerinea id. in Goldf. Petr. Germ. III, p. 45, Pl. 176, 
Fig. 11; and Peters, in Sitz. Akad. Wien, 1855, XVI, p. 361, Pl. IV, Figs. 1—3). Dr. Peters, 
indentifies with this species Zeuschner’s NV. depressa, but the proportions of whorls in the latter 
species, and of course of the animals respectively, agree rather with the Wer. depressa. 
