﻿JURASSIC AND TRIASSIC BRACIIIOPODA. 



131 



rounded in front. Some, on the contrary, are almost circular and about as broad as 

 long. 



The beak is either slightly incurved, or so much so as to overlie the umbone of 

 the opposite valve. The foramen which truncates its extremity is smaller in some 

 examples than in others, and the deltidium is scarcely ever visible. The dorsal valve is, 

 in the typical form, regularly, uniformly, and moderately convex, while in others it is 

 flattened or depressed at the umbone and towards the front. The greatest breadth of 

 the shell is usually towards the middle, but it is sometimes broadest anteriorly, while 

 tapering posteriorly. It varies in dimensions from two to three lines to two inches and 

 four lines in length. T. punctata occurs, in addition to the localities already quoted, in 

 the Zones of Am. Capricornus, A. margaritatus, A. spinatus (Middle Lias), and of A. 

 jurensis and A. opalinus (Upper Lias). 



The Rev. F. Smithe has found it in the Marlstone and in the Am. spinatus bed, and 

 indeed throughout the whole Middle Lias at Churchdown, in Gloucestershire, also in the 

 Cephalopoda-bed, or A. jurensis Zone, under the earthy ferruginous band in the Upper 

 Lias, at Havesfield Beacon in the same county. It occurs in the Am. Ibex Zone (Middle 

 Lias) at Churchdown, chiefly in geodes, which occur frequently in those clays, but the 

 matrix is so refractory that it is difficult to get them out in a complete condition (Smithe). 

 It may be quoted also from the Middle Lias at Willingore Cutting (new line from Lincoln 

 to Grantham), at Radstock &c. In Scotland, from the Island of Mull, Hallaig, Tobermory, 

 and Dunrobin. It occurs on the Continent in many localities where the Middle and 

 Upper Lias is represented. 



Mr. J. F. Walker is of opinion that T. sub-punctata should be retained as a variety 

 to include the large shell from the Marlstone of South Petherton. 



93. Var. Edwardsii, Dav. Dav., Ool. Mon., p. 30, PI. VI, figs. 11, 13, 14, and 15. 



Sufficiently described at p. 30 of my Monograph. It is very abundant in the Middle 

 Lias, or Zone of Am. margaritatus and A. spinatus, near Ilminster, and especially in the 

 first-named Zone at Churchdown, Gloucestershire (Rev. F. Smithe). 



94. Var. Radstockiensis. Sup., PI. XVI, figs. 14 — 18. 



Shell elongate, ovate, slightly rounded in front ; valves often very convex and inflated. 

 Ventral or larger valve uniformly convex, slightly deeper than the opposite one ; beak 

 large, thickened, very much incurved, and overlying the umbone of the opposite valve, 

 truncated by a small circular foramen. Dorsal valve very convex, slightly depressed near 



