LIOCERAS PINGUE. 67 



lateral and ventral areas. On the inner lateral area these radii are little more than 

 lines of growth ; on the outer they become small ribs, which, passing to the edge 

 of the ventral area, die away into very fine strias, and these unite on the carina at 

 a somewhat acute angle. Ventral area, broad and rather flat, forming a convex 

 surface broken by the small carina which runs along the middle. Inclusion 

 extending to the edge of the inner margin of the preceding whorl, and forming an 

 umbilicus regularly concave, except for a small recession where the body-chamber 

 is present. Inner margin slightly sloping and distinctly concave. The termination, 

 of which a slight portion is exhibited in PI. XII, fig. 1, is, as shown by other 

 specimens, strongly sigmoidal, like that of Lioc. formosum. 



This variety is one of those forms which require careful examination to dis- 

 tinguish them from the young of a different species. I have had figured on the 

 same plate (figs. 5 and 6) the young of Lioc. giganteum, which is the one 

 form with which this variety may be confounded. But that form possesses a 

 different umbilicus in which small steps are exhibited, because the whorls are 

 not entirely occluded. I have endeavoured to show the difference in the nature 

 of the umbilicus of the two specimens by the outline of the inner margins of the 

 whorls (figs. 3 and 7). Of course, with every whorl the difference in this respect 

 becomes more marked ; and if the specimen of Lioc. pingue had attained the same 

 diameter, but without the body-chamber being present, that is, if what is now body- 

 chamber had been filled with air-chambers, all its umbilicus would have been regu- 

 larly concave. The other chief difference between the two forms is the finer ribs 

 on Lioc. pingue. The difference in the sectional view has been exaggerated, by the 

 artist not having drawn enough inclusion in fig. 6. From all forms of Lioc. concavum 

 with sigmoidal ribs Lioc. pingue is separated by being much thicker, with scarcely 

 any carina ; whilst its sigmoidal ribs separate it from those forms of Lioc. v-scriptum 

 which it resembles somewhat in these respects. The nearest form to which it 

 approaches is that figured in PI. VIII, figs. 5 and 6 ; but this is not an adult of Lioc. 

 pingue, because it is narrower, especially at the ventral area, and has a sharper 

 carina, except on the body-chamber. One specimen of this variety in my collection 

 shows an unusual length of body-chamber for the genus, namely 0*67 of a whorl, the 

 normal amount being from 0*50 — - 55, rarely 0*60. Hitherto I have found that the 

 longer body-chamber accompanies the more compressed specimens ; but this is an 

 exception. 



Lioc. pingue is a scarce fossil ; it belongs to the Goncavum-beds of Halfway 

 House and Louse Hill only, and does not seem to occur at Bradford Abbas. It 

 is generally in a rather poor state of preservation. PI. XII, figs. 1 and 2, give a 

 very good drawing of this variety. The carina in fig. 2 is perhaps a trifle too 

 prominent. Fig. 3 shows a section of the regularly concave umbilicus. The 

 specimen is from Halfway House and in my collection. 



