﻿ADDENDA. 



203 



" 1. T. Arckiaciana, D'Orb. 1 horizon: A ^ , p 



. . ^Zoc. Varennes (Meuse), Perte 



Syn. T. Arckiaciana, Pictet and Renevier. , ^, . 



J J du Rhone. 



" 2. Triyonia, a small species which would include^ Horizon : Upper Greensand, 



PI. XXV, fig. 10. I Chloritic Marl, Gresvert. 



Syn. T. spinosa, Ag. 'Trig.,' PI. VII, fig. 6. [ Loc. Dunscomb Cliffs, Isle of 



? T. pumila, Nilsson. J Wight, and Warminster. 



" 3. T. Vicaryana, Lyc. PI. XXV, figs. 8, 9 ; Pl.l TJ . TT n , 



J J ' Horizon : Upper Greensand 



xxvra Ui la 3 ' and Chlorit ™- 



' . . ' .' ^-Zoc. Chardstock, Axmouth, 



Syn. T 7 . Arckiaciana, Pictet and Roux. Dunscomb Cliffs Great 



— — ' Morris Catal.,' 1854. | jjaldon 



— T. spinosa, D'Orb. J 



" No. 2 seems to occur sparingly in Dunscomb Cliffs, in company with T. Vicaryana, 

 from which it appears to differ in being smaller, more convex, and less elongated. It 

 appears (?) also to want the closely set series of small, oblique, supplementary costellso 

 on the upper half of the pedal border of the shell, which are very conspicuous in well- 

 preserved specimens of T. Vicaryana. 



" The third species (your T. Vicaryana) seems to be sufficiently distinguishable from 

 others of the spinosa group by its large size and (usually) more oblique outline. 



" It seems probable that the T. Arckiaciana, D'Orb., may have to be given up as a 

 British species, in so far at least as the Dunscomb and Great Haldon examples are 

 concerned." 



Trigonia Vicaryana, Lyc. Page 141, PI. XXIII, fig. 7; PI. XXV, figs. 8, 9; 



PI. XXVIII, figs. 4, 4 a ; PI. XL, figs. 3, 4. 



Recent researches of Mr. Meyer have shown that this species is abundant in the 

 Chloritic Marl of Dunscombe Cliffs, more especially in the beds 10 and 12 of his 

 classified section. See 'Quart. Journ. Geol. Soc.,' vol. xxx, p. 371. 



Mr. Vicary has also obtained specimens in the pebble-bed which overlies the Green- 

 sand at Great Haldon, where the species, although more rare, has the surface ornaments 

 preserved with great delicacy and beauty ; the little perpendicular pillars forming the 

 sides of the costae have great uniformity and prominence, but are scarcely depicted with 

 sufficient distinctness upon the magnified figure, PL XXVIII, fig. 4 a ; their upper 

 extremities are obtuse, forming upon each row a high narrow ridge bordering upon the 

 channelled base of each succeeding costa, features which are altogether distinct from the 

 plain step-like rows of costse depicted by D'Orbigny upon the magnified surface of 

 T. Arckiaciana. The specimen, PI. XXIII, fig. 7, tabulated T. Arckiaciana, proves to 

 belong to T. Vicaryana. Other small examples from the highest bed of the Haldon 



