AVICTJLOPECTEN FORBESII. 83 



T think it possible thai Pecten orbiculatus, a species founded on a right valve, 

 may belong- to the species under discussion, judging from the likeness of that 

 figure to the right valve of A. clathratus. 



/'. inter costatus, M'Coy, is a left valve of A. clathratus. The type is still 

 ] (reserved in the Griffith Collection, Museum of Science and Art, Dublin, where I 

 have examined it; but 1 cannot see the spines on the ribs which M'Coy regarded 

 typical of the species. They may have been there, and M'Coy states that " this 

 beautiful little shell appears very closely allied to P. inter stitialis, Phil]., but the 

 number of small ribs between every two large ones, instead of being regularly 

 three, is seldom less than five, and as frequently nine on the one specimen. . . . 

 It is seldom that any of the delicate spines are preserved, the ribs more frequently 

 presenting a roughened or tuberculated aspect." In the figured specimen (PL XV, 

 fig. 7) there appears to be three fine ribs between each pair of larger ones, and 

 not, as M'Coy states, five or nine. 



Avictjlopecten Foebesii, M'Coy, sp., 1844. Plate XVIII, figs. 3—7. 



Pecten Forbesii, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 93, pi. xv, fig. 20. 

 Avictjlopecten Forbesi, de Koninck, 1885. Abu. Mus. Roy. d'Hist. Nat. Belg., 



tom. xi, p. 223, pi. xxxv, figs. 14, 15. 



Specific Characters. — Shell small, suborbicular, slightly convex, the right valve 

 a little less so than the left valve. The margin fairly regularly rounded from ear 

 to ear. The hinge-line straight and comparatively long. Umbones small, pointed, 

 subcentral. The ears small, triangular ; the right anterior ear deeply slit for the 

 byssus ; the posterior ears larger than the anterior, the upper border prolonged 

 and pointed, posterior margin falcate. 



Intel ior. — Unknown . 



Exterior. — The surface is ornamented with strong radiating ribs, alternately 

 larger and smaller, the latter not starting at the umbo. The ribs are cancellated 

 by distant concentric ridges. The ears have a somewhat similar ornament. 



Dimensions. — PL XVIII, fig. 7, a right valve, the type of Pecten Forbesii, M'Coy, 

 measures — 



Antero-posteriorly . . . .10 mm. 



Dorso-vent rally .... 9*5 nun. 



Localities. — Ireland: the Carboniferous Limestone of Millicent, co. Kildare; 

 Little Island, co. Cork. Scotland : Currielee Quarry, Tvnewater. 



Observations. — This species was founded on a right valve, which is in the 

 Griffith Collection, Museum of Science and Art, Dublin. Curiously enough, the 



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