﻿88 BRITISH FOSSIL TRIGONIJ]). 



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 Trit/onice from the Kimmeridge Clay of the 

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

 Pleydell, Esq., of Longtliorns, near Blandford, Dorset, upon his pi'operty in the 

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



Strati^raphical 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, 2 «, 2 ^ ; PI. XIX, 



figs. \,\ a,\ b. 



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



1830, pi. xviii, fig. 1 . 



— — Damon. Geol. Weymouth, Suppl., ISfiO, pi. vii, fig. 2. 



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

 >• Portlandien des envir. de Boulogne, 



18G6, 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 boiuided at its upper 

 or umlional 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 ad nit forms its slight depression is the only feature which separates it from the 

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

 furrows ; these are much less conspicuous than in 1\ gibbosa ; like to that species the 



