AVICULOPECTEN IXTERMEDIUS. 81 



Aviculopecten tNTEEMEDius, M'Coy, sp., 1844. Plato XV, figs. 19, 20, 24, 25. 



Pterinea intermedia, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 82, pi. xiii, 



fig. 1. 



Specific Characters. — Shell small, triangularly gibbose, very slightly oblique 

 posteriorly; right valve unknown. The hinge-line long, produced posteriorly 

 along the pointed ear. The umbones narrow, gibbose, pointed, and placed a little 

 in front of the centre. The ears well formed and depressed, comparatively large, 

 the posterior much larger and deeper than the anterior ear ; the upper border of 

 the posterior ear prolonged and pointed, its posterior margin markedly falcate. 



Inferior. — Unknown. 



Exterior. — The left valve is ornamented with many fine, close, angular, radiating 

 ribs, which become larger and farther apart as they cross the valve ; and secondary 

 fine angular ribs arise between each primary pair. Towards the lower margin the 

 ribs are crenulate. The posterior ear has a few distant, obsolete, radiating lines, 

 crossed by concentric lines. The anterior ear has also almost obsolete radiating 

 ribs. 



Dimensions. — A small specimen from Hill Bolton, Yorkshire, in my collection, 

 measures — ■ 



Antero-posteriorly . . . .11 mm. 



Dorso-ventrally . . . .12 mm. 



Gibbosity of valve .... 2*5 mm. 



Localities. — England : the Carboniferous Limestone of Settle and Hill Bolton, 

 Yorkshire ; Castleton, Derbyshire ; and Poolvash, Isle of Man. Ireland : no 

 locality is given for this shell in Griffith's list of localities (Mourn. Geol. Soc. Dub.,' 

 vol. ix, p. 106). 



Observations. — This species was referred by M'Coy to Pterinea, but the long 

 posterior ear and the well-marked anterior ear show its affinities to be rather with 

 Aviculopecten than with that genus. I have been able to examine about half a 

 dozen specimens, one of which, from Settle, is in the Woodwardian Museum. This 

 (PI. XV, fig. 24) shows the posterior ear very well. PI. XV, fig. 10, represents the 

 left valve of a much younger shell, but unfortunately lacks the prolonged portion 

 of the posterior ear. 



The type specimen is not in the Griffith Collection at the Museum of Science 

 and Art, Dublin. M'Coy's description and figure, however, arc sufficiently dis- 

 tinctive and full, and there is no difficulty in recognising the peculiar characters 

 of the species. 



The ribs in older shells are coarse, irregular, and tend to be compound and to 

 lose the crenulate marking of the younger stages. 



