﻿ADDENDA. 187 



forms have their analogues or are even identical with Cotteswold species of the Supra- 

 liassic Sands. 



Professor Oppel also (' Juraformation,' p. 400) referred T. pulchella to the lower 

 portion of the Inferior Oolite, of which he regarded it as a characteristic species ; he 

 recorded its occurrence at Gundershofen (Bas Rhin), Milhau (Aveyron), and Metz 

 (Moselle). 



It is only recently that T. pulchella has become known as a British species ; its 

 discovery in a lower stratigraphical position has resulted from the persevering researches 

 of Mr. Keeping, of the Woodwardian Museum, Cambridge, who obtained specimens in the 

 Upper Lias at Bracefield brick-pits, near Lincoln, associated with Ammonites serpentiniis, 

 A. bifrons, A. communis, and other Ammonites special to that zone. The Lincoln 

 specimens are smaller than those figured by Agassiz, and by Quenstedt in his ' Der Jura ;' 

 they agree better with the figure given by the latter author in his ' Handbuch der Petre- 

 factenkunde,' tab. 43, fig. 14. It has not been obtained at any other British locality. 



Trigonia affinis. Miller. PI. XXI, fig. 7, also PI. XL, fig. 2 (Glabra). 



Tkigonia affinis. Sow. Min. Conch., tab. ccviii, fig. 3, vol. 3, 1818. 



The description of this species and also of T. excentrica given at pages 94 and 95 

 require to be supplemented by the revised present description. 



Shell short, convex mesially, umbones not prominent, erect, anterior side produced 

 and rounded, hinge-border short, its outline slightly convex, curved elliptically, with the 

 posteal extremity, which is obtusely rounded. The sides of the valves have numerous 

 small regular subconcentric costse which have prominence anteally even to the border ; 

 they disappear rather suddenly about the middle of the valve, and the posteal half of 

 the shell is plain ; the posteal slope is slightly flattened and is distinct only near to the 

 apex. The lines of growth are only slightly defined ; there are three arrests of growth, 

 which are also only obscure. The hinge characters have not been exposed. 



The specimen, Plate XL, fig. 2, contributed by Mr. Vicary, has the length 31 lines, 

 the height 24 lines, the convexity of a single valve 7J lines. 



Compared with T. excentrica the general figure is larger, much shorter, or more 

 equilateral ; the umbones have less prominence, the costse are more numerous, imperfectly 

 developed, and nearly approach the concentric figure. Specimens of advanced growth 

 acquire much thickness and their costse become evanescent. For the most part the 

 specimens upon the tablets of our Greensand Collections, both public and private, are 

 very indifferently preserved and are not separated from specimens of T. excentrica. 



Positions and Localities. The specimen figured, PI. XL, fig. 2, was obtained by Mr. 



