﻿COSTATA. 



• 165 



contain specimens of T. pullus, which are scarcely larger than the head of a pin. The 

 Wiltshire Cornbrash, more especially at Hilperton, near Trowbridge, has produced a 

 multitude of examples in a fine condition of preservation ; the species is also present in the 

 northern extension of the Great Oolite at Appleby, Lincolnshire ; near to which locality 

 it has been collected and recorded by the Rev. J. E. Cross. It is unknown in the Corn- 

 brash of Yorkshire. 



Sowerby figured a group of small costated forms from Cutch as examples of T. pullus 

 (' Geol. Trans.,' 2nd series, vol. 5, plate 21, figure 7), but as the escutcheon and area are 

 not clearly exposed the identity of the species remains doubtful. 



A small area and escutcheon figured by Quenstedt ('Der Jura,' tab. 67, fig. 13), 

 as T. costata from the highest member of the Great Oolite at Einingen, undoubtedly 

 represents T. pullus. 



Trigonia monilieera, Ag. Plate XXXI, figs. 1,1 a, 1 b, 2, 2 a, 10. 



Trigonia costata, Goldfuss. Petrefacta Germanise, tab. cxxxvii, fig. 3 c, 1836. 



— monilifera, Agassiz. Mem. sur les Trigonies, p. 40, tab. iii, figs. 4 — 6, 



1840. 



— ? parvula, Agassiz. Idem, tab. xi, fig. 8, young example. 



— papillata, Agassiz. Idem, p. 39, tab. v, figs. 10 — 14. 



— reticulata, Agassiz. Idem, pi. xi, fig. 10. 



— monlifera, cTOrbigny. Prodrome de Paleontologie, vol. i, p. 365, No. 293, 



1850. 



— — Quenstedt. Der Jura, p. 759, 1858. 



— — Damon. Geology of Weymoutb, Suppl., pi. iv, fig. 1, 1860. 



— marginata. Idem, pi. vi, fig. 8 (mould of the interior). 



— costata, Greivingk. Gest. u. Geol. Livonia und Courland, Dorpat, 1864. 



Shell ovately trigonal, very convex, both mesially and anteally, umbones prominent, 

 much incurved, and more or less recurved ; anterior side moderately produced, rounded, 

 its border curved elliptically with the lower border, its superior or umbonal portion is 

 slightly excavated ; hinge-border concave, its length is one fourth greater than that of 

 the siphonal border, with which it forms a considerable angle. The escutcheon is very 

 wide and concave, its surface is for the most part delicately reticulated, having two series 

 of numerous small fine ridges ; the series occupying only the anteal portion of the surface 

 passes transversely across the escutcheon, the posteal series takes the direction of the 

 lines of growth ; these are also delicate and decussate the anteal series. The area is of 

 moderate size, distinctly bipartite, somewhat concave, and is nearly alike in both the 

 valves ; the plane of its surface forms nearly a right angle with the costated portion of 

 the valve, it has a prominent median carina, and larger bounding carina) ; the marginal 

 carina is prominent in both the valves, its indentations are small but are conspicuous 



