The Invertebrate Fauna of the Uitenhage Series. 203 



most advanced stage represented in this individual, in which the 

 ultimate whorl is not complete anteriorly. The greatest breadth 

 falls at the umbilical rim, and in section the ultimate whorl is very 

 broad in relation to its height ; the peripheral area forms a broadly 

 flattened arch. The umbilical wall falls very steeply and abruptly 

 from the rounded rim, and the relatively narrow umbilicus has the 

 form of a profound and acutely pointed funnel. 



The umbilical ribs, commencing above the spiral suture, are 

 narrow, and they are slightly backwardly directed as they pass up 

 into the compressed and fairly prominent marginal tubercles. There 

 are sixteen of these flattened tubercles in the ultimate whorl, and 

 from them the secondary costae proceed mostly in regular groups of 

 three, though from two of the nodes four ribs are given off. The 

 secondary ribs follow a direct course from the nodes across the 

 periphery except near the anterior part of the whorl, where a few 

 of them appear to have a very slight forward inclination. This, 

 however, may possibly be due to an accident of preservation, 

 and may stand in relation to a slight distortion exhibited by the 

 specimen in its anterior part. The ribs crossing the periphery 

 are fairly prominent, and at the anterior part of the peripheral 

 area the crests of adjacent ribs are situated at 4 mm. apart from 

 one another. On the last whorl there is a single deeply impressed 

 constriction. 



In this specimen the shell is in great part preserved, and the 

 course of the septal sutures remains unknown. The ultimate whorl 

 seems to comprise a part at least of the body-chamber. 



Dimensions. 



Greatest diameter 80 mm. 



Greatest breadth of the last whorl in cross-section 68 



Height of the last whorl at the centre, in section 25 ,, 



Greatest diameter of the umbilicus, measured from the 



umbilical rim between the tubercles 28 ,, 



Occurrence. The specimen is from the Modder Drift, Sunday's 

 Eiver, and is preserved in the collection of the Geological Society of 

 London (registered 10976). 



Remarks. The specimen here described was thought by Pavlow 

 to represent H. schenki (Oppel). It bears a label " Ammonites 

 baini Sharpe, Jurassic, Modder Drift, S. Africa. Dr. Atherstone, 

 F.G.S., 1876," and the descriptive details given by Pavlow (op. cit., 

 p. 493) apply to it accurately. I am convinced that this African 

 form is so characterised that it cannot rightly be united with 

 H. schenki, and though it appears highly probable that the two are 



