LIOCERAS FALLAX. 79 



Lioceras fallax, 8. Buckman. Plate XIV, figs. 10, 11. 



Discoidal, compressed, subcarinate ; whorls subconvex, ornamented with coarse, 

 broad, rounded, subfalciform ribs, projected forwards on the ventral area, more 

 conspicuous on the outer than on the inner area, nowhere very distinct, but 

 appearing more like large undulations on the sides. Ventral area narrow, and 

 acutely sloping towards a carina, which, though seemingly much elevated, is not 

 really very distinctly separated from the sloping ventral area. Inner margin 

 concave but rather upright. Inclusion over about three-fourths 1 of the whorl. 

 Umbilicus evidently very open in youth, but more closed in maturer age. It 

 exposes portions of the inner whorls with an appearance somewhat tumid owing 

 to the ends of the ribs being present. 



Lioc. fallax is in general shape and proportions very much like Lioc. giganteum ; 

 but there are many characters of ribbing, coiling, &c, which seem to point to its 

 being really more distinct than would at first be supposed. It is possible that 

 badly-preserved specimens of this species and of Lioc. giganteum would be difficult 

 to separate ; but it is always better to reject badly-preserved examples since they 

 frequently lead to erroneous ideas. I consider that the ornamentation and mode 

 of growth exhibited by this species preclude any idea of its being a descendant, 

 of Lioc. giganteum. In youth it evidently possesses, judging from the inner 

 whorls, an umbilicus more open and also flatter than that of Lioc. giganteum, and 

 yet has those portions of the whorls visible in the umbilicus more tumid. At a 

 little later period the umbilicus becomes somewhat contracted and appears 

 deeper, owing to the presence of a rather upright inner margin (the inner margin 

 is more sloping against the body-chamber, but is drawn rather too much so 

 in the figure). This is the time when, the umbilicus being somewhat similar 

 in size, this species has most resemblance to Lioc. giganteum. But, after all, 

 its broad coarse ribs, few in number, its whorls, with their more pronounced 

 slope from the middle towards an ill-defined ventral area, and its larger carina, 

 separate it very distinctly. The latter characters and the larger umbilicus 

 separate it from Lioc. v-scriptum, the thick form. Its ribs have somewhat the 

 same coarse character as those of that variety, but are subfalciform and somewhat 

 more prominent. Altogether this species is rather more distinct than any other 

 species of Lioceras, and seems somewhat isolated. Its descent is not clear. I 

 do not think it has come from Lioc. giganteum on account of the reasons which I 

 have given. It is more in character with the Lioc. v-scriptum forms ; but we do 

 not know whether its ribs are V-shaped or otherwise in youth. Its carina is 



1 In the figured specimen it is about two-thirds owing to the recession of the inner edge of body- 

 chamber. 



