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BRITISH FOSSIL TRIGONLE. 



appear also that the rows of costae have a greater curvature upwards towards the carina 

 than obtains in the specimen figured by Contejean. 



Stratigraphical position and Locality. The specimen upon which our description is 

 founded is deposited in the Museum of the University of Oxford, and was obtained in 

 the Portland Limestone of Shotover Hill; it is of less advanced growth than the 

 specimen figured by Contejean, and still less so than the one figured by De Loriol ; the 

 area and its bounding carinas are only indifferently preserved, so that their little plica- 

 tions are not shown. 



For this addition to the Trigonia of the Portland formation I am indebted to the 

 liberality of the late Professor Phillips, who obtained and forwarded to me well-executed 

 plaster casts of all the Trigonice in the Geological Museum of the University of Oxford. 



Increased knowledge of the Clavellata of the K'immeridge Clay has led me to regard 

 the specimen figured, Plate IX, fig. 2, and there given as a supposed variety of T. incurva, 

 as referable rather to a variety of T. Alina, Cont., having fewer costae than the shell of 

 the Portland Oolite, but possessing no other distinctive feature. 



Trigonia Hudlestoni, Lye, sp. nov. PI. XXXIV, figs. 5, 6 ; PI. XXXIX, figs. 1 a 



and 2 (Clavellat^e). 



Shell ovately trigonal, depressed, excepting the posterior slope which is steep and 

 convex. Umbones prominent, pointed, nearly erect ; anterior side very short, its border 

 curved elliptically with the lower border ; hinge-border straight, lengthened, sloping 

 downwards, forming less than a right angle with the anterior border. Area narrow, 

 flattened, transversely delicately plicated ; marginal carinas small, minutely and densely 

 tuberculated, excepting upon its lower third, where the tubercles disappear, and it 

 becomes plicated or obscurely nodose ; inner carina large, transversely prominently 

 plicated ; median carina small and distinct, represented at the upper half of the shell by 

 a row of minute, closely placed tubercles, which become obsolete over the lower half of 

 the area. Escutcheon depressed, somewhat excavated, flattened obliquely, irregularly 

 plicated ; its length is considerable, or exceeding half the length of the entire valve ; no 

 part of its surface is visible when a valve is placed horizontally and viewed from above. 



The rows of tuberculated costae are about eighteen in the fully developed form ; they 

 are narrow and elevated with about twelve or thirteen tubercles in each row, the rows 

 are widely separated, have little curvature, their carinal extremities become nearly per- 

 pendicular and are much attenuated and imperfectly subnodose or cord-like. 



The most prominent distinctive features in this large species consist in the short 

 depressed, subtrigonal form, the narrow area, its steep slope; the widely separated 



