﻿UNDULAT.E. 57 



•when figured and described in the ' Monograph of the Great OoUte Mollusca/ published 

 by the Pateontographical Society in 1853, it was only known as a British species from a 

 single specimen indiilerently preserved, and not sufficiently exhibiting the characteristic 

 features ; it was obtained at Trewsbury Quarry, in Forest Marble, near to the Tetbury 

 Road Station of the Great Western Railway, near to Cirencester. More recently the 

 Rev. J. E. Cross has obtained fine examples in the upper subdivision of the Great Oolite 

 at Thornholm, near to the Village of Appleby, Lincolnshire ; to the liberality of that 

 gentleman I am indebted for the specimens now figured. Mr. Cunnington has also 

 kindly forwarded to me four specimens from the Combrash of Hilperton, near Trowbridge ; 

 Hinton, in the same county, is another locality. 



Fine examples of T.fleda have also been obtained in the Great Oolite of Marquise, 

 near to Boulogne ; they constitute the T. angiilata of D'Orbigny and of Oppel. 



Trigonia paucicosta, Lycett, sp. nov. Plate XI, figs. 8, 9 ; Plate XVI, fig. 7. 



Shell ovately oblong, convex ; umbones moderately elevated, antero-mesial, and 

 recurved ; anterior side rather short, its border curved ; lower border much more 

 lengthened, with a lesser curvature ; superior border lengthened, somewhat concave, 

 sloping obliquely, forming a conspicuous angle with the posteal border of the area. 

 Escutcheon narrow, slightly depressed, its superior border somewhat raised. Area 

 narrow, flattened, divided 1)y a mesial furrow, bordered by a minute row of tubercles, 

 bounded by two small distinct carinse, which have each a row of tubercles ; those of 

 the marginal carina are large, regular, widely separated, and somewhat compressed by 

 the lines of growth, they become evanescent upon the posteal half of the valve in 

 specimens of advanced growth, upon which portion the surface has conspicuous irregular 

 transverse plications ; in the young shell the area has a few plain transverse costeUse. 

 The costae upon the other portion of the surface consist at first, of three or four naiTow, 

 elevated, plain, somewhat angulated ridges, which become, near to the carina, sub- 

 tuberculated ; subsequently they form two series, the anteal series are narrow, distinctly 

 ridged, irregularly knotted or sub-tuberculated, they are nearly straight, and pass 

 obliquely downwards to the middle of the valve, when they meet with a much larger, less 

 numerous, posteal series of nodose varices ; this posteal series turns upwards suddenly at 

 a considerable angle to the anteal series, towards the carina, from which the varices are 

 well separated, and with which they form right angles. In adult forms the lower portion 

 of the valve has the anteal costae more irregular, and the junction of the two series is 

 less angulated or more obscure ; the whole aspect becomes influenced by the folds of 

 growth which are conspicuous. Some specimens which scarcely constitute a distinct 



