﻿RHYNCHONELLA. 



107 



ribs, which do not appear to have been grooved along the middle, as is the case with those 

 of the last-named species. 



Loc. B. jlexistria is not a very common species ; it occurs in the Carboniferous lime- 

 stone of Bolland, Clitheroe, and in several Derbyshire localities, &c. In Ireland, Mr. Kelly 

 mentions Millecent, Rahoran, and Knockninny. I am not acquainted with any Scottish 

 specimen, nor is it known to me from any Continental locality, although it is no doubt to 

 be found in several. 



Rhynchonella angulata, Linnaus (sp.) PI. XIX, figs. 11—16. 



Anomia angulata, Linnceus. Systema Naturae, i, pars ii, p. 1154, 176/. 

 Tekebratula excavata, Phillips. Geol. Ycrks., vol. ii, p. 223, pi. xii, fig. 24, 1836. 



— angulata, De Eoninck Animaux foss. de la Belgique, vol. i, p. 284, pi. 



xix, fig. 1, 1843. 



Rhynchonella angulata, UOrbiyny. Prodrome, vol. i, p. 146. 1 

 Hemithvris angulata, M'Coy. British Palaeozoic Fossils, p. 439, 1855. 

 Anomia angulata, Hanley. Ipsa Linnaei Conchylia, p. 133, 1855. 



Spec. Char. Elongated, sub-trigonal or cuneiform, rarely as wide or wider than 

 long, the greatest breadth at a short distance from the front ; valves sometimes much 

 flattened, but assuming every degree of convexity, and even gibbosity. The lateral 

 portions of the beaks in both valves are much depressed, forming large, broad, flattened 

 spaces, which extend to upwards of half the length of the shell ; the beak of the ventral 

 valve is moderately produced, tapering to a point, nearly straight, or but feebly incurved ; 

 foramen small, margined by a deltidium. The dorsal valve is convex and sharply incurved 

 at the umbone, almost straight towards the front, the lateral portions of the valve sloping 

 rapidly on either side. The surface is smooth close to the umbone, but soon becomes 

 ornamented by from six to nine large angular plaits, of which two, three, or four com- 

 pose the mesial fold, while one, two, or three strongly curved plaits occupy each side of 

 the lateral portions of the valve. The ventral valve, when viewed in profile, presents a 

 very convex curve from the beak to the extremity of the sinus, this last being in 

 general rather shallow, and composed of one, two, or three angular ribs. Measurements 

 taken from three individuals have presented — 



Length 12, width 9|, depth 7 lines. 

 10 fi 7i 



j> 10, ,, 11 ,, S ,, 



Obs. This remarkable but variable shell may always be distinguished from other 



1 This appears to be the only species belonging to the genus Rhynchonella D'Orbigny would admit 

 in the Carboniferous period, all the other species of this genus are placed by him in the genus Atrypa ! 



