476 BRITISH PALAXOZOIC FOSSILS. [ LAMELLIBRANCHIATA. 
slightly convex from the beak to the anterior lateral angles; sides flattened, and sometimes the middle of the 
front depressed ; often three diverging sulci from the beak to the front margin, forming obscure ridges on the 
exterior. Surface with close, irregular, minute plications of growth. Length of small example five lines, greatest 
proportional width near the anterior end, 4 in the short valve, © in the long valve. 
The wide, short, oblong form of this species easily distinguishes it from the others in the upper Paleozoic 
rocks. The more elongate, narrow, oblong species well figured in Portlock’s Geol. Rep. t. 32. f. 5, under this 
name, might be called LZ. Portlocki (M°Coy); its proportional width is only = in the long, and % in the short 
valve. 
Position and Locality —Not uncommon in the black carboniferous limestone of Carluke, Lanarkshire. 
3rd Class) LAMELLIBRANCHIATA (See page 256). 
ist Ord. Pirvroconcua (See page 257). 
3rd Family. PECTINIDA. 
Shell inequivalve, inequilateral, solid (not foliaceous), regular or subregular, fixed by a byssus or by the 
substance of the valve ; hinge-line straight and usually eared ; pallial line entire, outside the adductor ; one large, 
oval, muscular impression near the middle on the anal side of each valve; cartilage small, internal, in a pit 
beneath the beak; hinge with or without teeth. Animal: the margin of the mantle fringed with fleshy con- 
tractile filaments, studded at regular distances with brilliant eye-like tubercles ; foot rudimentary, slender, clavate, 
with a bundle of fibres or byssus at the base; mouth with lips; gills very large, of few filaments. 
Differs from the Liming in being inequivalve, in the oculiform tubercles, and the internal cartilage (not 
exposed in a notch). 
Genera: 1, Pecten ; (including as subgenera Amusium, Hinnites, and Janeria) ; 2, Spondylus ; 3, ? Plicatula ; 
the two latter having hinge-teeth, no byssus, and being attached by the substance of the valve, form the Fam. 
Spondylide. 
Genus. PECTEN (Brug.) 
Gen. Char.—Shell depressed, the upper valve most convex, slightly inequilateral ; beaks contiguous; hinge- 
line produced into ears on each side of the beak, the anterior largest, and separated from the body of the shell 
in the lower valve by a deep notch for the passage of the byssus; ligament of two distinct parts, one internal in 
the triangular pit beneath the beak, the other external, forming a narrow line along the hinge-margin ; with or 
without radiating hinge-teeth. 
This genus contains as subgenera, first, the above described type; 2nd, Janira; 3rd, Amusium; 4th, 
Hinnites; 5th, Pedum. The two latter are identical in shell and animal with Pecten when young; Hinnites 
becomes afterwards distorted and fixed by the lower valve, and Pedum is distorted from growing in corals (not 
fossil). The genus has not been yet quoted from the lower Paleozoic rocks; I doubt its occurrence in the 
Devonian ; and the greater number of those shells hitherto called Pecten in the carboniferous rocks, I now find 
to have no cartilage pit, and by other characters to form a particular genus of Aviculidw ; they are common in 
the oolitic rocks, and increase in number to the present day. I leave with doubt in this genus a few carboni- 
ferous species with the anterior ear longer than the posterior, and the internal structure of which I have 
not seen. 
