440 INFERIOR OOLITE AMMONITES. 



specimen may be compared with Sonn. modesta, juv. (PL XCVI, figs. 1, 2) ; but 

 it is costate at an earlier age. The degree of inclusion prevents it being placed as 

 the young of a large number of somewhat latumbilicate species. 1 



Sonninia, sp. Plate XOV, figs. 9, 10. 



This little form possesses costaa and subbullicostas about as 3 to 1. The only 

 species to which it bears any likeness is Sonn. densicostata ; and it appears to 

 have whorls which are rather too thick to allow its being placed as the young of 

 that form. 



Sonninia, sp. Plate XCVII, fig. 5 (suture-line only). 



For comparison with the suture-lines of Sonn. dominans (p. 435) the septal 

 margin of an immature, externally very similar fossil was illustrated in PI. XCVII, 

 fig. 5. It shows that identification by external appearance only would be 

 extremely hazardous. The specimen is an ally of Sonn. revirescens (p. 417), as 

 may be learnt by a comparison of the present figure with fig. 9 of PI. C, though 

 the terminal lobule of L is shown isosceloid in the former ; but this is due to the 

 septal margin being only imperfectly shown after the filing-away of test. The 

 specimen only differs from Sonn. revirescens by a broader and flatter periphery. 

 From crassa it differs in mode of coiling and in having connate costae. The 

 specimen is from Bradford Abbas. 



Sonninia, sp. Plate CIII, fig. 19 (suture-line only). 



This fossil is similar in external appearance to Sonn. simplex and Sonn. 

 subsimplex ; but it is remarkable for the extreme difference in septation and the 

 extraordinary complexity of its long and involved lobes. These characters 

 almost suggest its inclusion in the longilobate series II D, B (p. 430) ; but there 

 is a certain difference in the character of the terminal lobule ; and, further, the 

 specimen is thinner than any of that series. The shell is from Bradford Abbas. 



1 In estimating umbilication in young forms the greatest care is necessary. A millimetre differ- 

 ence between two young specimens may become 10 or 20 mm. difference in their respective adults. 

 This applies also to other dimensions. 



