BIVALVIA. 133 



less produced, and the height is much less than in that shell ; it is more nearly allied to, 

 but is more oblique, than a large lias species which is not uncommon in Gloucestershire 

 and Oxfordshire. Height and diameter through both the valves equal, lateral diameter 

 one fourth more. The specimen forwarded to us from Yorkshire is much smaller than 

 several which we have obtained in the Cotteswolds, in one of which the lateral diameter 

 exceeds two inches. 



Geological position and localities. — The Great Oolite of Scarborough ; also in the 

 middle or freestone beds of the Inferior Oolite in Gloucestershire ; but it has not occurred 

 in the Great Oolite of the same county. 



Unicardium depressum, Phil. sp. Tab. XIV, fig. 10. 



Cokbula depressa, Phil. Geol. York., 1, t. 9, f. 16. 



Testa ovato subglobosa ; umbonibus magnis, subanticis incurvis, margine cardinali oblique 

 declivi subrccto, basi et lateribus rolundis ; plieis concentricis crebris irregularibus et 

 inaqualibus. 



Shell ovately globose, oblique ; umbones large, depressed, anterior to the middle of the 

 valves ; hinge border sloping obliquely downwards and nearly straight, its posterior ex- 

 tremity rounded ; the margins of the valves, basal, anterior, and posterior, rounded ; the 

 general figure tumid, excepting near to the hinge border, where the surface is more de- 

 pressed ; the surface is covered with closely-arranged concentric plications which are irregular 

 and unequal. 



The substance of the test is of greater thickness than is usual in this genus ; it is most 

 nearly allied to U. varicosum, p. 73, tab. 8, figs. 7 — 8 ; but it is much more oblique and 

 of greater length, the dimensions being, height, 14 lines ; length, 17 lines ; there is some 

 amount of variation in the obliquity of the valves and we have specimens which exhibit 

 greater obliquity than the example from Yorkshire. 



Geological position and localities. — The grey limestone of the Great Oolite at Scar- 

 borough. In Gloucestershire it has occurred only in the Inferior Oolite in the bed called 

 Trigonia Grit. 



Trigonia dkcorata, Lye. Tab. XV, fig 1. 



Trigonia decokata, Lycett. Ann. and Mag. Nat. Hist., 1853, vol. xii, pi. 1 1, f. 1. 



Testa ovato trigona, subcompressa, umbonibus obtusis, non recurvatis, area cardinali lata 

 -plana tripartita; carina interna tuberculis in varicis elongatis instructus, carina media et 

 marginali tuberculis minimis crebris ornatd : lateribus tuberculis per series arcuatis 

 concentrice dispositis. 



Shell ovately trigonal, somewhat depressed ; umbones obtuse, not recurved ; anterior 



