70 INFERIOR OOLITE AMMONITES. 



ventral process is not greatly developed. What may have caused this retardation 

 I cannot at present say, but that it was no detriment to the forms which possessed 

 it, may be seen from the fact that those with V-shaped ribs are certainly more 

 numerous in the Bradford-Abbas district than those with sigmoidal ribs. The V- 

 shaped character of the ribbing is not confined to Lioc. v-scriptum ; but the forms 

 which I have united under this name certainly show it in a marked degree. 

 Besides this character, they also have a rather flat and broad ventral area, with a 

 small carina which is necessarily less distinct than if the ventral area were as much 

 sloped as it is in the type. 



What we must call sub-varieties of Lioc. v-scriptum are met with — for instance, 

 one form with a much smaller, quite concave umbilicus. Of this I have figured a fine 

 large adult as Lioc. concavum, var. A, 1 PI. YI ; but I believe the above is its proper 

 position. A young specimen of this form is figured 2 in PI. IX, figs. 5, 6. This 

 sub-variety is scarce, and I have not had many specimens to examine ; the adult 

 specimen, being too large, does not show the reflexed ribs. 



Another sub-variety has a larger, deeper, and yet regularly concave umbilicus, 

 and is considerably thicker. An adult specimen of this, PI. X, figs. 5, 6, shows 

 the change from V-shaped to sigmoidal ribs very clearly, which change takes place 

 when the shell has a diameter of about four inches. In this form the inner margin 

 is deep, the concave depression of the inner area is broad and not very perceptible, 

 while the whorls slope towards the external edge from the middle of the lateral 

 area. 



Lioc. v-scriptum is most likely to be confounded with forms of Lioc. concavum ; 

 but the V-shaped ribs, less compressed appearance, and small carina on a flattish 

 ventral area, should distinguish it. Young specimens which, having the body- 

 chamber, exhibit some tendency to recession from the line of coil at the period 

 when the change from more open to narrower umbilicus usually takes place, are 

 easily confounded with specimens of Lioc. apertum. Such a one is figured in PI. 

 X, figs. 7, 8 ; and a form somewhat intermediate between Lioc. v-scriptum and Lioc. 

 concavum, exhibiting a similar tendency, in PI. XV, figs. 5, 6. The difference con- 

 sists in Lioc. apertum having coarser ribs and a definitely larger umbilicus, which 

 remains constant in size at the different ages ; while the umbilicus of these forms of 

 Lioc. concavum and v-scriptum exhibits an accidental resemblance, though only at a 

 certain period of growth, owing to the recession of the inner margin on account of 

 the presence of the body-chamber. Of course the close relationship between Lioc. 

 v-scriptum and Lioc. apertum is apparent. Either they may be descended from a 

 common ancestor, or Lioc. apertum may be an instance of a sub-variety of Lioc. 



1 Por " var. A " substitute " var. v-scriptum." 



2 Its carina, especially in fig. 6, is drawn too prominent, giving to the specimen the appearance of 

 another variety. 



