LIOCERAS CONCAVUM, VARIETIES. 75 



k. (PL X, fig. 9.) Similar to 0, but the inner area is much compressed ; peculiar 

 raised ridges on the middle of the lateral area ; ribs strongly recurved. Unique 

 specimen ; Bradford Abbas. 



2. Carina nearly obsolete. 



X. (PI. VI j 1 PL IX, figs. 5, 6.) Small umbilicus. Bradford Abbas. 



/u. (PL IX, figs. 1, 2; PL X, figs. 6, 7, 8.) This is a slightly thicker form; 

 umbilicus larger. Fairly numerous, especially when small. Bradford Abbas. 



v. (PL X, figs. 5, 6.) Still thicker; larger umbilicus. Fairly numerous. 

 Bradford Abbas and Halfway House, Dorset ; and Stoford, Somerset. (X, ft, and 

 v form the variety Lioc. v-scriptum.) 



o. (PL XV, figs. 5, 6.) Much compressed ; sides nearly parallel ; open 

 umbilicus. Scarce. Bradford Abbas. 



In the forms a, (5, y, and S the acuteness of the carina and ventral area decreases 

 in this order ; but e, t have the ventral area very acute. The adult of n is very much 

 like the type ; but its umbilicus is regularly concave. It is rather doubtful 

 whether it has more claim to be placed in the Class I or in II. Its ribs are certainly 

 much projected on the lateral area, and form a rather acute angle ; but at the same 

 time they are projected slightly on the ventral area, and very soon (when the 

 diameter is about two inches) become subfalciform. Some young specimens 

 (when the diameter is about half an inch), if I am right in placing them here, 

 show strongly-marked V-shaped ribs. The specimens included in are exactly like 

 Lioc. v-scriptum but have a sharper ventral area and more prominent carina. The 

 ribs change when the diameter of the shell is about three inches. 



In Plate IX, figs. 8, 9, 10, an abnormal form is depicted. This really belongs 

 to t. From some cause one side (fig. 9) shows no concave inner margin, but a 

 much larger umbilicus and some strong depressions ; while fig. 10 illustrates the 

 difference which the front view exhibits. (This is not the only case of malfor- 

 mation which I have met with.) The test is perfectly preserved over the whole 

 specimen, and so there can have been no crushing during fossilisation. 



The annexed Table I will show at a glance the greater or less similarity in 

 shape between the various forms which I have mentioned. It should, however, 

 be borne in mind that those which are placed in an intermediate position may not 

 be intermediate in the strict sense of the term, that is, they may not be in any 

 way intermediate in point of descent. Possibly an intermediate form possesses 

 characters which its neighbours do not show, and was not the descendant of the 

 one, or the ancestor of the other. This arrangement may not be natural, but 



1 Erase the words " var. A " on Plate VI, and substitute " Variety v-scriptum." 



