68 BRITISH POSSIL TRIGONI^. 



examples arc figured on Plate XI, figs. 6, 7. In the absence of better illustrative 

 specimens it is therefore necessary to cancel " T. minor" as this obscure form was desig- 

 nated in the list of Inferior Oolite Trigoniaj, page 13 of this Monograph. 



The internal mould is not known ; impressions occur in the Ferruginous Oolite of 

 Glaizedale, North Yorkshire. All the localities are in Inferior Oohte. 



Trigonia subglobosa, Lye. Plate XII, figs. 8, 9, 10. 



Trigonia subglobosa, Lycett. Ann. and Mag. Nat. Hist., 1850, p. 421. 



— — Morris and Lycett. Gr. Ool. Monog., Pal. Soc, 1853, p. 55, 



pi. V, fig. 21. 



— — Morris. Catal., 1854, p. 229. 



An inflated shell with prominent ornamentation and nodose angulated costae. 

 Shell ovately globose ; umbones antero-mesial, large, produced, much incurved, and 

 slightly recurved ; anterior and inferior borders curved elliptically ; posterior or superior 

 border short, concave, its posteal extremity forming an obtuse angle with the posteal 

 border of the area. Escutcheon wide, depressed, and rather short. Area wide, flattened, 

 slightly excavated, its surface forming a considerable angle with the other portion of the 

 shell ; it is conspicuously bi-partite, the lower constituting the larger portion ; it is 

 traversed transversely by irregular rugose plications, which near to the apex are replaced 

 by a few, narrow, regular, plain costellge ; it is bounded by tuberculated carinae ; the 

 tubercles upon the marginal carina are unusually large and nodose ; the median carina is 

 also represented by a similar, but smaller row of tubercles. The other portion of the 

 shell has upon its anteal side thirteen or more, narrow, depressed, subtuberculated costae, 

 which are rather irregular in their course, but, for the most part, curve obliquely down- 

 wards to within a short distance of the carina, when they meet with a much larger and 

 more prominent nodose posteal series, fewer in number (about eight or nine), which pass 

 upwards perpendicularly to the carina, their point of junction with each of the anteal 

 series having a large tubercle ; the angles thus formed are more considerable than right 

 angles. Upon the lower third of the adult valves the plications of growth become 

 strongly marked anteally, and all other ornamentation then ceases ; this change is also 

 accompanied by a sub-concentric sulcation which crosses the valve longitudinally. 



Affinities. It is allied to a larger species, T. Painei, Lye, in the general features of 

 its ornamentation, but is greatly more inflated; the area is much wider and more 

 ornamented, and more especially by the presence of the prominent marginal carina with its 

 few large tubercles ; this latter feature, together with the absence of large transverse plica- 

 tions upon the area, and its sub-globose figure, serve also to separate it from T. conjungens. 

 The valves are separate, or spread open and held in contact by their ligament. 



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