LAMELLIBRANCHIATA. | UPPER PALZEOZOIC MOLLUSCA. 489 
AVICULOPECTEN PLANO-RADIATUS (M°Coy). PI. 3. E. fig. 8. 
Ref.=1d. M°Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. 
Dese.—Ovate, apical angle 80° in young specimens, 95° in adults from an upward curve of the anterior 
side; length and width nearly equal; gently convex, most so at one-fourth from the beak; beaks narrow, pro- 
minent; ears on each side yery deeply defined from the body of the shell by narrow, very steeply-inclined 
planes, flattened; left anterior one rotundato-quadrate, obscurely radiated, very deeply divided from the body 
of the shell by an abrupt vertical, slightly concave space extending to the beak; posterior ear longer, fal- 
cately pointed, radiated by a few slender ridges crossed by the lines of growth; surface radiated with numer- 
ous ribs (thirty to forty at one inch and a half from the beak), which are smooth, broad, flat, or slightly convex, 
more or less irregular in width, and separated by a very narrow impressed line towards the margin and body of 
the shell, but nearer the beak they are sharp, narrow, and alternately larger and smaller, ten in one line at two 
lines from the beak, but each rib varying from one to two lines wide at two inches from the beak, separated 
only by very narrow impressed lines; the ears are sharply striated, parallel with the margin, and have a few 
narrow distant radiating ridges. Width from beak to ventral margin from one and a half to nearly four 
inches, proportional length =, depth of left valve =. 
The radiations vary from one and half lines to half a line wide in different specimens at the margin. 
The species differs from the P. planicostatus (M°Coy) in not being oblique, and the much greater number of 
its ribs. 
Position and Locality —Common in the carboniferous limestone of Derbyshire. 
Explanation of Figures.—P1. 3. E. fig 8. Left valve natural size, of specimen broken along the ventral 
margin. 
AVICULOPECTEN RUTHVENI (A/’Coy). PI. 3. E. fig. 4. 
Reef. =1d. M*Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. 
Desc.—Rotundato-quadrate, suborbicular; apical angle about 110° in the adult, from the upward curve 
of the sides, only 95° in the young; length slightly exceeding the width, tumid; surface radiated by about 
fifteen thick, rugged ridges, between each pair of which are usually three (rarely seven) smaller ridges, each 
pair of which are separated by a concaye space about equal to the thickness of the ridges; ears large, the 
posterior one broad, extending as far as the margin of the shell, with three or four distant radiating ridges, 
crossed by coarse lines parallel with the concave extremity; anterior ear similar, but slightly smaller, both 
defined by a rather rapid flattening from the body of the shell. Width from beak to opposite margin about two 
inches, length (at right angles to the width) about the same, proportional depth of one valve =. 
Fragments of this species bear some resemblance to portions of the Pecten? quinquelineatus (M°Coy), 
but it is distinguished by the much less number of the ridges, &e. I have dedicated this species to John Ruthven 
of Kendal, the well-known enthusiastic collector of Palzeozoic fossils. 
Position and Locality. Rare in the impure carboniferous limestone of Dent, and one small specimen from 
the similar limestone of Lowick. 
Lxplanation of Figures.—P1. 3. E. fig. 4. Left valve; natural size. 
AVICULOPECTEN SEGREGATUS (J7°Coy). PI. 3. E. fig. 1. 
Ref. and Syn.= Pecten segregatus M*Coy, Syn. Carb. Foss. t. 17. f. 3. 
Dese.— Ovate or rotundato-subtrigonal ; apical angle 75°; right valve slightly convex, left one conoidal, very 
gibbous, most so at one-third from the beak; front rounded, dorso-lateral margins deflected nearly at right angles 
to form a steep concave boundary from the ears; ears unequal, very deeply defined from the body of the shell, 
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