﻿104 BRITISH FOSSIL TRIGONI^. 



TiUGONiA PULLUS, Sow. Platc XXXIV, figs. 7, 7 a, 8, 9. 



Tkigo.m.v pullus, Soic. Min. Conch., tab. dviii, figs. 2, 3, 1826. 



— — Agassiz. Trigoiiies, p. 9, 18-40. 



— — d'Orhignij. Prodrome dc Pak'out., vol. i, p. 308, 1850. 



— cosTATA, var. PTJLLtrs, Morris and Lycett. Monogr. Great Oolite, Part II, 



p. 58, tab. I , fig. 22 (Palseont. 

 vol. for 1853), 1853. 



— PULLUS, Morn's. Catalogue, p. 229, 1854. 



— COSTATA, Quenstedt. Der Jura, p. 502, tab. Ixvii, fig. 13, 1858. 



— — Park., var. pullus. Sharp. Oolites of Northamptonshire, Quart. 



Journ. Geol. Soc., vol. xxvi, p. 

 388, 18/0. 



— 11. sp., near to pullus, J. E. Cress. Geology of N. W. Lincolnshire, 



Quart. Journ. Geol. Soc, vol. 

 x.xxi, p. 125, 1875. 



— COST.VTA, var. vvllvs, Jiidd. Mem. Geol. Survey, Rutland, &c., pp. 151, 



155, 161, 220, 281, 1875. 



Shell ovately trigonal, convex ; umbones prominent, acute, and recurved ; anterior side 

 moderately produced, its border curved elliptically with the lower border ; hinge-border 

 nearly straight, sloping obliquely from the postcal extremity of the escutcheon to that of 

 the marginal carina. The escutcheon is wide and concave, delicately impressed by a 

 twofold kind of ornamentation ; its anteal portion has a series of small depressed costella3, 

 which pass across the surface transversely ; the posteal portion has more obscure, oblique 

 costelloe, which take the direction of the lines of growth ; both series of costellae are wrinkled. 

 The area is wide, the plane of its surface forms a considerable angle with the costated portion 

 of the valve ; it is bounded by two well-marked carina?, of which the inner carina is small, 

 but distinctly dentated ; the marginal carina is large ; plain and smooth near the 

 apex; its middle and posteal portions are more or less plicated. The surface of the area 

 is somewhat concave, divided into two portions by a mesial depression ; and in the young 

 state it has also a distinct median carina, which posteally can usually only be considered as 

 one of the costellae which ornament the surface ; posteally these costellae become merged 

 in the folds of growth ; the right valve has the area divided into two portions, but 

 has no distinct median carina ; the costellae arc fewer and larger than in the other valve.. 

 The other portion of the valve has the costae large, closely arranged, and rounded ; their 

 attenuated extremities are simply curved upwards to the anterior border : the largest 

 specimens, about eighteen lines in length, have twenty costae. 



The peculiarities of the escutcheon in T. jmllus supplies the most clear distinctive 

 feature separating it from other small examples of the Costata. 



Positions and Localities. — In the Inferior Oolite the shelly freestones of Leckhampton 



