LIOCERAS BRAD FORD EN SE. 25 



Lioceras bradfordense, var. giganteum, S. Buchman. Plate XI, fig 1 ; Plate XII, 



figs. 4—7. 



Adult. — Discoid, subcarinate, whorls somewhat compressed, slightly subconvex, 

 ornamented with mere lines of growth ; ventral area sloping towards a small, hardly 

 distinct carina. Inner margin regularly concave and sloping. Inclusion consider- 

 able, normally nearly three-fourths of the preceding whorl. Umbilicus rather deep 

 on account of the absence of any depression on the inner area, and regularly 

 showing portions of the inner whorls. 



Immature. — At a diameter of about two inches (Plate XII, figs. 5, 6, 7) : — 

 whorls slightly subconvex, ornamented with not very prominent, simple, sigmoidal 

 ribs, which are obscure on the inner area. Ventral area smooth and flat, with a 

 small, barely distinct carina. Inclusion two-thirds. Umbilicus small and deep, 

 showing portions of the inner area of each whorl down to the centre. 



At a diameter of about six inches : — ribs single, commencing to become obscure, 

 especially on the inner area. Ventral area smooth, with the carina somewhat more 

 prominent at this age than any other. Inclusion three-fourths of preceding whorl. 

 Umbilicus showing a portion of the inner area of each whorl, which portions exhibit 

 at first some small ribs but are now becoming smooth. 



The thickness of this variety and its small, deep umbilicus, mark it off as a form 

 which must necessarily attract attention, and at first sight cause it to seem very 

 different from either of the other forms of Lioceras bradfordense. I say other forms 

 because, to be quite correct, I ought to notice that, in reality, with this one 

 there are figured three forms of Lioc. bradfordense, showing certain differences 

 from each other. Of the typical variety (at least the one which I had in view when 

 I first mentioned the fossil 1 ), an immature specimen is figured, Plate IV, figs. 5, 6 ; 

 on Plate V a slightly thinner form with wider umbilicus is figured, which, to speak 

 with great precision, is not the more adult form of Plate IV, figs. 5, 6, but of 

 fig. 7 ; while opposed as it were to this form, but seemingly more distinct from 

 the typical form, is the one we are now treating of, much thicker and with a small, 

 deep umbilicus. The thick and the thin forms seem to be more peculiar to the 

 Beaminster district, while my specimens of the intermediate or typical forms come 

 from Bradford Abbas. Between this form and Ludwigia Murchisonce there can 

 hardly be any chance of that confusion which, as I have already shown, may possibly 

 occur between the thin form and that species on account of their remarkable con- 

 vergence in some respects. A comparison, however, of these forms of Lioceras 

 bradfordense with Ludwigia Murchisonce on one side and with Lioceras concavum 



1 ' Quart. Jouro. Geol. Sue.,' 1881, p. 601. 



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