198 
large, triangular, and nearly flat, the deltoid fissure is rather large, and the 
beak small, pointed and slightly recurved. Both valves are nearly equally 
convex. The dorsal valve is usually ornamented with five, rarely with seven, 
angular folds, of which the central fold representing the dorsal ridge is a 
little more pronounced than the others, and corresponds to the ventral furrow. 
The ventral valve has six folds like those of the dorsal valve. The whole 
surface is furnished with fine concentric, imbricated plates, and the shell is 
perforated. 
Dimensions. — The length is four, the breadth five, and the thickness 
three, millimetres. 
Delations and Differences . — This species differs from the preceding 
by its less curved form, and the development of its hinge area, also by the 
small number and the arrangement of its folds. It hears some resemblance 
to that Spirifer of the Tournai Limestone which I at first confounded with 
S. heteroclytus, Lefrance, and which is figured by d’Orbigny under the 
name S. Koninchiamis in his “ Prodrome de Paleontologie,” This Spirifer 
which Mr. T. Davidson mistook for this species differs from it by being 
shallower, and above all by the complete absence of the concentric plates 
which cover the surface of S. insculptus, plates which are replaced by 
undulations of growth. 
Horizon and Localities. — This species usually accompanies the pre- 
ceding, and like it belongs principally to the upper beds of the Carboniferous 
Limestone. A single specimen of it was found by Mr. W. B. Clarke in a 
brown, compact, ferruginous limestone at Colocolo. I have given the 
dimensions of this. 
Genus — CYRTINA, T. Davidson. 
Cyrtina septosa, J. Thillips. 
PL XV, Pig. 2. 
Spirifera septosa, .T. Phillips, 1S3G, G-eol. Tortshire, II, p. 216, pi. 9, %. 7. 
Spirifer suheonicus, L.-G. de Koninck, 1845, Descr. Anim. Poss. Terr. Civrb. Pelg., p. 255, 
pi. 12 bis, fig. 5 (non Martin). 
