﻿228 INFERIOR OOLITE AMMONITES. 



inner margin is represented as slightly concave ; and its sutures have a longer 

 superior-lateral lobe. No front view is given ; but the front view of his fig. 3 

 certainly seems to represent a thicker fossil. 



Taking Zieten, pi. vi, fig. 1, as the type of Mayer's Am. opalinoides, there is 

 certainly considerable resemblance between " opalinoides " and " Sinon," but the 

 ventral area of the latter is evidently much more acute, and the ribs are stronger. 



The most interesting fact about Hudl. Sinon is the manner in which its outer 

 whorl prefigures the other species of the genus. It is easy to imagine Hudl. 

 serrodens as the descendant of this species, although it is more probably derived 

 from Hudl. affinis. The specimen figured (PI. XXXVIII, figs. 13 — 16) is in the 

 collection of Mr. W. H. Hudleston, F.R.S., who kindly lent it, and others, for this 

 work. It came from the Grey Sands, Blue Wyke, Yorkshire. 



Hudlestonia affinis 1 (Seebach). Plate XXXVIII, figs. 1 — 8. 



1864. Ammonites affinis, Seebach. Der bannoverische Jura, pi. viii, figs. 4 a, b. 



Adult : Discoidal, compressed, carinate. Whorls with strongly gibbous sides, 

 their convexity interrupted near the ventral edge by a slight depression. 

 Ventral edge narrow, slightly rounded. No defined inner margin. Inclusion 

 apparently about three-fourths of preceding whorl. Sutures simple with broad 

 lobes. 



Young : Whorls ornamented with subsigmoidal, ventrally-inclined radii, which 

 are sometimes united on the inner area, forming a coarser rib. Ventral area 

 more pronounced, with a carina on the core. 



The material of this species is not only lamentably fragmentary, but is in the 

 form of poor casts. In sectional view the whorls differ somewhat from Seebach's 

 figure, being less convex altogether, and especially near the inner margin. In 

 Seebach's figure the whorls are more pear-shaped in section ; in our specimens 

 they are almost lanceolate. 



The forms figured by Brauns and Schloenbach 2 do not seem to me to 

 represent Seebach's species. Schloenbach's figure, especially, appears to be much 

 too compressed and too involute, and in this respect closely resembles Hudl. 

 serrodens. Brauns' figs. 1, 2, appear to have the same features ; but his outline 

 fig. 3 is rather gibbous, although not so gibbous as Seebach's. Of course, as 

 Hudlestonia serrodens is probably only the compressed, involute development of 



1 The name " affinis" "near to," probably refers to its relationship to Am. serrodens. 



2 See the synonyms of Hudl. serrodens. 



