88 BRITISH FOSSIL TRIGONI^. 



The size is usually smaller than T. Bamoniana. 



Dimensions of a specimen rather smaller than usual : 



Length 22 lines, height 18 lines, diameter through the united valves 14^ lines. 



The name is intended as a slight recognition of most welcome assistance rendered to 

 the author by the loan of some interesting TngonicB from the Kimmeridge Clay of the 

 Cliffs of Dorsetshire, one of the results of extensive explorations made by J. C. Mansel- 

 Pleydell, Esq., of Longthorns, near Blandford, Dorset, upon his property in the 

 Kimmeridge Clay, a formation which has been but little exposed in England. 



Stratigraphical position and Localities. — T. Manseli has occurred somewhat rarely in 

 the Limestone of the Isle of Portland and Tisbury. Specimens are in the Museum of 

 Practical Geology, Jermyn Street ; in the collection of Dr. Wright, of Cheltenham ; in 

 the collection of Mr. Cunnington, of Devizes ; also in my own cabinet. 



Trigonia Damoniana, de Lor. PI. XVIII, fig. 3 ; PI. XX, figs. 1, 2, ^a,2b; PI. XIX, 



figs. 1, 1 a, 1 ^, 



Trigonia gibbosa, a new variety, Etherelda Benett. Catal. Org. Rem. County of Wilts, 



1830, pi. xviii, fig. 1. 



— — Damon. Geol. Weymouth, SuppL, 18G0, pi. vii, fig. 2. 



— Damoniana, de Loriol and Pellat. Monog. Paleont. et Geol. de I'etage 



Portlandien des euvir. de Boulogne, 

 1866, pi. xvii, figs. 4, 5. 



Shell sub-ovate, lengthened obliquely, convex, umbones large, erect, very prominent 

 and somewhat pointed, much incurved and rendered bipartite by the narrow deep 

 sulcation produced by the apical termination of the ante-carinal space ; borders of the 

 valves elliptically rounded, excepting the hinge-border, which is straight and lengthened, 

 sloping obliquely ; the anterior face of the valves has also a large, rounded, depressed 

 space or lunule, which gives a slightly truncated aspect to that portion when viewed 

 laterally. The escutcheon is depressed, cordiform, and strongly marked by the lines of 

 growth ; the area is narrow, slightly elevated or convex, traversed transversely by irre- 

 gular folds of growth ; it has a well-marked mesial furrow, and is bounded at its upper 

 or umbonal portion by two rows of minute, sparsely-arranged tubercles ; some specimens 

 have also a median line of minute tubercles bordering upon the groove ; more frequently 

 these three lines of carinal tubercles cannot be traced or only partially so even upon well- 

 preserved specimens. The anti-carinal space or sulcation is narrow, smooth, and only 

 slightly depressed, excepting near to the umbones, where it forms a deep sulcation ; more 

 frequently in adult forms its slight depression is the only feature which separates it from the 

 area. The costated portion is divided into three or four zones by as many elliptical horizontal 

 furrows ; these are much less conspicuous than in T. gibbosa ; like to that species the 



