LAMELLIBRANCHIATA. | UPPER PAL-EOZOIC MOLLUSCA. 479 
opposite margin. A line connecting the apices of the two ears would lie nearly half their length above 
the beak. 
Position and Locality—In the carboniferous limestone of Derbyshire, and Lowick ; in the carboniferous 
shale of Craige, near Kilmarnock. The original Irish localities are, in the yellow sandstone of Bruckless; 
common in the carboniferous slate of Linsapaste; Calp of Bundoran, Ballintrillick. 
Family. AVICULID (See page 257). 
Genus. PTERINEA (See page 258). 
PTERINEA? INFORMIS (J/°Coy). 
Ref. = Avicula id. MeCoy, Syn. Carb. Foss. Irel. t. 18. f. 21. 
Dese.—Obliquely trigonal, very gibbous from the beaks to the respiratory margin, from which line the sur- 
face arches rapidly towards both the dorsal and yentral margins; no defined posterior slope: posterior wing 
flattened, slightly pointed, extending nearly as far as the posterior end of the shell; its posterior margin 
moderately concave; posterior end obtusely rounded; ventral margin moderately convex; byssal sinus small, 
variable, at about one-third the length from the anterior end; anterior end very small, rounded; beaks very 
large, tumid, prominent ; surface with two or three large, obtuse, concentric, rounded wrinkles or waves of 
growth, near the posterior end. Length from beak to posterior margin about eight lines, greatest proportional 
width at right angles to middle of hinge-line about %, depth of left valve 5%, length of posterior wing about ;%,, 
width thereof ; one rather thick posterior lateral tooth running a little below a greater part of the length of 
the hinge-line. 
The few obtuse wrinkles on the posterior portion of the shell, and its general bluntness of form, distin- 
guish this species from the more nearly allied ones. The originally described specimens were smaller than the 
present examples, which have also the extremity of the posterior wing rather more pointed than in my above- 
cited figure ; the anterior end in all our specimens is unfortunately broken off, so that I have not seen the great 
anterior adductor impression, and have therefore some slight doubt of the genus. 
Position and Locality —Not very uncommon in the carboniferous limestone of Poolwash, Isle of Man, 
PrERINEA L#VIGATA (A/‘Coy). 
Ref. and Syn. = Avicula id. M°Coy, Syn. Carb. Foss. t. 13. f. 28. 
Dese.— Obliquely falciform, trigonal, gently and moderately convex from the beak towards the respiratory 
margin, from which line the surface slopes gradually to the ventral margin, which is much curved and to the 
dorsal margin, which is undefined and nearly straight: posterior wing flattened, but not separated from the 
body of the shell by a defined posterior slope ; its posterior margin concave, the apex extending about half 
the length of the shell in old specimens, rather more in young ones; beak moderately gibbous ; anterior side 
forming a short rounded lobe; an obtuse byssal sinus at the anterior third of the ventral margin, from whence 
a shallow concavity extends towards the beak; surface nearly smooth, with a few lines of growth, coarsest at 
the edge of the byssal sinus, sharp and regular, parallel with the end of the posterior wing. Posterior adductor 
impression large, shallow ; anterior adductor impression a little below and in front of the beak, transversely oval, 
deep, strongly marked ; two or three minute accessory impressions extend from the anterior adductor to the 
beak ; no hinge-teeth, hinge-line narrow. Average length three inches, greatest transverse proportional width 
65 
from ventral margin to middle of dorsal slope at right angles thereto j, width of posterior wing =, length 
thereof about 2, length of anterior side about 4, depth of left valve ;;. 
This fine shell bears some resemblance to Gervillia lunulata of Phillips, but is easily distinguished by its 
greater size, wider posterior end, smooth surface, and the total absence of the steep posterior ridge, which in 
[Fasc. 11. ] 
