60 MOLLUSCA FROM THE GREAT OOLITE. 



Localities. Everywhere in the shelly beds of the Minchinhampton district ; in the 

 Forest Marble of Wiltshire and Dorsetshire. 



Trigonia costata, Sow., var. elongata. Tab. V, fig. 23. 



Somewhat rarely an elongated variety of this well-known form occurs in the shelly 

 beds of the Great Oolite ; it is somewhat more convex than T.puUus, the marginal carina is 

 remarkable for its general straightness and prominence, the costae are less curved and are 

 disposed with greater obliquity than in the other varieties, and the character of the area 

 has nothing peculiar. It is not distinguishable from a shell from Cutch, figured and 

 described by Mr. Sowerby in the ' Geological Transactions,' 2d ser., vol. v, pi. 21. 



Trigonia flecta. Tab. V, fig. 20. 



Testa ovato-trigond, subcompressd, area elongata, planatd, transverse striata ; carinis 

 ejusdem subnuUis, superficie costis angustis, horizontalibus rectis, postice angulo Jlectis, 

 angulo costarum subrecto. 



Shell ovately trigonal, or oblong, rather compressed, area elongated and flattened, 

 transversely striated ; carinse scarcely distinguishable, the middle portion of the area with a 

 longitudinal furrow ; the other portion of the shell with narrow straight nearly horizontal 

 costse, which at their posterior portions are suddenly bent upwards at a right angle, and 

 become nodose, forming short perpendicular varices. 



It differs from T. angulata. Sow., in the absence of tuberculated carinse upon the area, 

 in its flatness and in the costse, which are more closely arranged, and have not the elegant 

 curvature of the Inferior Oolite shell. The general figure is more oblong than T. 

 Goldfussii and T. undulata, Agassiz, to both of which it has a certain resemblance in the 

 character of its surface. It would seem to be rare ; we have only met with a single 

 example, which occurred in a rock too hard to permit the perfect exposure of the shell ; its 

 position is a bed somewhat shelly and situated a little beneath the Bradford clay. 



Locality. The Tetbury Road station of the Great Western Railway. 



Trigonia duplicata, Sow. Tab. VI, fig. 2. 



Trigonia duplicata, Sow. Min. Con., t. 237, f. 4, 1819. 



Testa ovato-trigond antice rotundatd, postice productd et rostratd, umbonibus obtusis 

 sub-recurvis ; ared angustatd transversd striatd, medio sulco longitudinali, carinis parvis 

 tuberculis mi?iimis instructis ; costis serratis ornatis ; costulis prioribus concentricis et 

 regularibus, aliis obliquis nonnunquam dichotomis. 



Shell ovately trigonal, moderately convex, anterior extremity rounded, posterior 

 extremity produced and rostrated, superior border rather concave; umbones mesial, 



