﻿C2 BRITISH FOSSIL TRIGONL^. 



Messieurs Terqucm and Jourdy have figured, under the name of T. prodi/cia, a small 

 species of the Clcwellata from tlic Great Oolite of the Department of the jMcselle (' Mem. 

 Soc. Geol. Fr.,' 2 ser., torn, ix, lbC9, pi. xi, figs. 29, 30), this is aUied to, and perhaps 

 is not really distinct from, T. impressa, Sow. 



StraUgrapldcal position and Localilies. T. j)foducta is one of the rarer fossils of 

 the Trigonia-grit of the Inferior Oolite, near to Cheltenham and to Stroud ; fine 

 examples have also been obtained in Northamptonshire by the officers of the National 

 Geological Survey. Specimens from the Inferior Oolite of Normandy are in the British 

 Museum. 



Trigonia conjuncens, mil. PI. X, figs. 5, 7, 8 ; PI. XIII, fig. 6. 



TitiGONiA CONJUNGENS, Phillips. Geol. Yorks., 1829, vol. i, p. 156. 

 — — Morris. Catal., 1854, p. 228. 



Shell ovately oblong, moderately convex mesially, somewhat depressed near to the 

 anterior and posteiior borders; umbones elevated, obtuse, erect, or slightly recurved, 

 placed within, or in other specimens upon, the line of the anterior third of the valves ; 

 anterior border produced, curved elliptically with the lovi^er border; hinge-border 

 straight, lengthened, sloping obliquely, and terminating posteally in the wide, rounded, 

 posteal border of the area. Escutcheon large, lengthened, depressed, excepting its 

 superior border, Avhich is raised. Area very wide, occupying about one third of the 

 surface of the valve ; it is somewhat raised, expanded, and flattened posteally ; it has 

 a well-marked mesial oblique furrow, and is traversed transversely by numerous large 

 plications, which increase in size posteally, and become irregular, prominent, and 

 wrinkled (see Plate XIII, fig. 6); the bounding cariuEe are small and distinct; the 

 marginal carina is minutely plicated, excepting its posteal portion, which is occupied by 

 the large transverse plications of the area ; these form small varices upon the inner 

 carina ; there is no median carina. The costated portion of the valve has numerous rows 

 (eighteen or nineteen in adult forms) of tuberculated or sub-tuberculated costae, the first- 

 formed six or seven rows are very closely arranged, regular, plain, nearly horizontal, 

 and slightly curved at their two extremities : those which succeed form two series ; the 

 anteal series are somewhat irregular in their arrangement, but are always small and 

 inconspicuous ; they are directed somewhat obliquely downwards to the middle of the 

 valve, and are occasionally distinctly tuberculated, but commonly are irregularly sub- 

 tvd)crculated ; their posteal extremities are united about the middle of the valve to 

 another, less numerous, and somewhat larger posteal series of costae, which are also either 

 distinctly tuberculated or sub-tuberculated ; they approach the carina at a considerable 



