﻿RHYNCHONELLA. 



109 



acquainted with but a single certain synonym, that of excavata, published by Professor 

 Phillips in 1836. 



The original example of B. angulata is still preserved in the Linnean collection, where 

 it has been compared by myself, as well as by several of our London Palaeontologists. I 

 am also of the opinion expressed by the late Mr. Sharpe, that B. angulata, of Sowerby, 

 found in the Jurassic strata of England, is specifically distinct from that of Linnseus, and 

 must receive another denomination. 



Loc. B. angulata does not appear to be a very abundant fossil ; it is found in the 

 Lower Scar limestone of Yorkshire and of the Isle of Man. In Ireland it is stated by 

 Mr. Kelly to occur at Ardagh, and abundantly at Ardelogh ; but I am not acquainted 

 with any Scottish example. On the Continent it has been collected by Professor De 

 Koninck from the Carboniferous limestone of Vise, in Belgium. 



Rhynchonella (?) trilatera, De Koninck. PI. XXIV, figs. 23 — 26. 



Terebratula trilatera, De Koninck. Animaux fossiles de la Belgique, p. 292, pi. xix, 



fig. 7, 1843. 



Rhynchonella trilatera, Morris. Catalogue of British Fossils, 2d ed., p. 148, 1854. 



Spec. Char. Shell sub-triangular or sub-quadrate, with the angles rounded ; valves 

 almost equally deep, convex, and flattened along the middle ; a slight median depression 

 or groove, originating at the extremity of the beaks, in either valve, extends at times to the 

 frontal margin. The beak of the ventral valve is acute, very small, and generally closely 

 adpressed to the uinbone of the opposite one ; the lateral portions of the beaks in either 

 valve are flattened or compressed, while the frontal margin is nearly straight, from the 

 total absence of all sinus or fold. From sixteen to eighteen angular ribs ornament the 

 surface of either valve, while the five or six central are generally much larger than lateral 

 ones. Interior unknown. Two examples measured — 



Length 4|, width 5, depth 3 lines. 



J> < J J »» °) 55 ^2 55 



Obs. This remarkable species, of which no British specimen has till now been figured, 

 does not appear to have ever attained much larger proportions than those above given, and 

 is easily distinguishable from its congeners by the peculiar shape and character of its shell. 

 It varies somewhat in the degree of convexity or flatness of its valves, and the median 

 groove or depression is more or less apparent. The dorsal valve is more often flatter than 

 the ventral one ; the ribs also either diminishing regularly in width from the centre, or 

 having the middle ones (comparatively) much larger than those that cover the lateral 

 portions of the valves. 



None of the interior characters being at present known, the shell is provisionallv 



