CARBONIFEROUS FOSSILS OF IRELAND. 101 



Pecten transversus. Sow. 



Pecten transversus. Sow. Geol. Trans. — Pecten transversus. P//I/. Pal. Poss. 



Sp. Ck. — Transversely oval, slightly convex ; ears moderate, nearly equal, acute; surface with strong 

 radiating ridges, disposed in about twenty-six fasciculi of three each, each bundle being distinctly separated 

 from the adjoining ones ; entire surface marked witli fine, sharp, concentric striae. 



This species resembles the P. Knockonniensis, M'Coy, which see : the specimens wliich have occurred 

 are very impeifect. 



Pecten tripartitus. M'Coy. (PI. XVI. fig. 8). 



Sp. Ch. — Longitudinatoly ovate, longer than wide, slightly convex; ears very unequal, one small, square, 

 the other very large, roimded; sides finely and sharply striated longitudinally ; middle of the shell smooth. 



This species has its surface divided longitudinally into three portions, the two outer of which are delicately 

 striated, and the middle one smooth ; this is much more distinct in some specimens than in others, but is always 

 perceptible ; the ears are very unequal, tlic small one smooth, the larger with coarse, radiating strias. Length 

 four lines, width three lines. 



Pecten uNDULATus. M'Coy. (PI. XVIL fig. 12). 



Sp. C/i . — Elongate, ovate ; ears unequal, posterior one small, pointed, anterior large, rounded, deeply divided 

 from the body of the shell ; surface with numerous, equal, fine, concentric striae, decussated by radiating striae 

 similar to the transverse ones in shape and size, but rather farther apart ; three or four short, round plaits in the 

 posterior side-margin. 



Tliis species is rendered very remarkable by the short, obtuse folds or plaits in the posterior margin, and 

 I have found the character constant in six or seven specimens which came to hand of tlie species, they appear 

 very characteristic ; the whole surface is beautifully reticulated, with sliglitly flattened, delicate strise. Length 

 ten lines, width nine Hnes. 



Pecten variabilis. M'Coy. (PL XVI. fig. 7). 



Sp. C/i. — Shell smooth; ears unequal; anterior ear square at its extremity, narrow; posterior ear rectan- 

 gular, undefined ; form varying from longitudinally ovate to orbicular, and from sHghtly convex to globose. 



The normal character of this very variable species appcai-s to be a longitudinally ovate form, the length, 

 however, but little exceeding the breadth, moderately convex, and perfectly smooth ; but among the countless 

 varieties some are nearly flat, others almost hemispherical ; some shew a plication of the surface, longitudinal, 

 obhque, or concentric, and some extreme varieties are even wrinkled or undulated concentrically ; these are, 

 however, obviously the abnoirmal conditions ; the parts about the beak or the ears are not liable to variation. 

 Lengh eleven lines, width nine lines. 



MoNOTis. Bronn. 



Gen. Ch. — Suborbicular, inequivalve; usually rounded anteriorly; auricidated posteriorly; ears un- 

 defined. 



Those shells differ from Pecten in having their ears usually undefined, and very frequently no ear on the 

 anterior side, whence their name. 



MoNOTis ^QUALis. M'Coy. (PL XV. fig. 1). 



Sp. Ch. — Suborbicular, length and width equal; hinge-line less than the width of the shell; right valve 

 convex, posterior ear pointed, anterior ear small, rounded ; left valve flattened ; body of the shell radiated with 



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