78 CARBONIFEROUS LAMELLIBRANCHIATA. 



Aviculopecten peea, M'Coy, sp., 1844. Plate XV, figs. 13 — 15. 



Pecten pera, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 97, pi. xv, fig. 19. 

 Non Aviculopecten peea, M'Coy, 1855. Brit. Pal. Foss., p. 488. 



Specific Characters. — Shell small, quadrato-ovate, inequivalve. The left valve 

 more convex than the right ; slightly oblique. Ears large, deep, and well defined ; 

 the anterior rectangular, the larger ; the posterior pointed. The lower margin 

 rounded ; the posterior border more oblique than the anterior border. The hinge- 

 line straight, moderately long. The umbones triangular, moderately gibbose, 

 pointed, subcentral. 



Interior. — Unknown. 



Exterior.-— The left valve is ornamented by numerous irregular, often unequal, 

 radiating ribs, obscurely nodular at intervals, especially towards the margin, often 

 alternately large and small. The anterior ear has many radiating ribs, crossed by 

 concentric lines of growth ; the posterior ear has fewer thicker radiating ribs. The 

 right valve is almost smooth, but towards the margin there is evidence of fine 

 radiating ribs. 



Dimensions. — PI. XV, fig. 14, a left valve in the collection of the Geological 

 Survey, Jermyn Street, No. 7256, measures — 



Antero-posteriorly . . . .21 mm. 



Dorso-ventrally . . . .21 mm. 



Localities. — England : the Carboniferous Limestone of Wetton and Narrowdale, 

 Staffordshire. Ireland : the Carboniferous Limestone of Town Plots, Killala. 



Observations. — The specimen labelled Pecten pera in the Griffith Collection, 

 Museum of Science and Art, Dublin, can hardly be the original type, for it is much 

 larger than the figure. M'Coy re-described this species and referred to it some 

 shells from the Black Limestone of Derbyshire ; but if these be the shells labelled 

 A. pera in the Woodwardian Museum, he has confused A. Knochonniensis, M'Coy, 

 with the Pecten pera of his previous work. 



Remarking on the specimens in the Woodwardian Museum, M'Coy makes the 

 following curious statement : — " From the greater perfection of the English 

 specimens, I have no doubt a portion of the ventral margin must have been absent 

 in the specimens I originally figured, making the ears appear too large." Only 

 one specimen appears to have been figured. It is thus difficult to determine this 

 species with certainty, owing to the confusion by its author of two descriptions 

 based on differenl shells, and by the loss of the type. I rely on the original 

 description, and especially on the character of the ears, which M'Coy states to be 



