(j6 carboniferous lambllibranchiata. 



and finer in size, still nodulose. The anterior ear is crossed by radiating ribs, 

 separated from the valve by a hollow space marked by concentric lines. On the 

 posterior ear the ribs are large and further apart than on the valve. 



Dimensions. — PL VIII, fig. 8, a specimen from Settle, in the "Woodwardian 

 Museum, Cambridge, measures — 



Antero-posteriorly . . . .61 mm. 



Dorso-ventrally . . . .68 mm. 



Localities. — England : the Carboniferous Limestone of Settle, Yorkshire ; 

 Castleton, Derbyshire; Lowick, Northumberland. 



Observations. — P. Dumontianus is more coarsely ribbed than P. granosus, and 

 the ribs are not so regularly punctate. It is not so gibbose as A. Ruthveni. Frag- 

 ments may be easily mistaken for A. Murchisoni, but the latter has markedly 

 alternate strong and fine nodular ribs, while its hinge-line is comparatively short, 

 with both ears, especially the posterior, well defined and much depressed. I have 

 fortunately obtained a specimen with both valves (PI. VIII, figs. 5, 5 a), whereas 

 hitherto only the left valve has been described. The ornamentation varies to a 

 considerable extent in different individuals. A fine specimen with both A^alves, in 

 the Manchester Museum, Owens College, is figured on PI. XIV, figs. 1, 2. 



Genus Aviculopecten, M'Coy, 1851. 



Avicttlopecten, M'Coy, 1851. Aim. Mag. Nat. Hist., 2nd ser., vol. vii, p. 171. 

 — (pars), 1854. Brit, Pal. Foss., p. 392. 

 Hall, 1883. Pal. N. York, vol. v, pt. i, Lamell., p. xii. 

 Non Zittel, 1900. Text-book Palceont. (Trans.), p. 380. 



Generic Characters. — Shell inequivalve, almost equilateral, ovate. Umbones 

 well marked, swollen, and pointed, especially in the left valve. Ears well defined 

 and large, the posterior often produced along its upper border and pointed. Hinge- 

 line moderately long. 



Interior. — The hinge-plate is striated longitudinally and very narrow. The 

 adductor scar is large, and placed high up in the valve and posterior to the 

 middle line. 



Exterior. — The surface of the valves is ornamented with radiating ribs and 

 concentric lines, more or less well marked, and often nodular, punctate, or 

 imbricated. The right valve nearly always marked somewhat differently from the 

 left. The ears always marked by few radiating ribs, separated by smooth, holloAv 

 spaces, which show fine concentric lines of growth. 



Observations. — The type species of Aviculopecten, M'Coy, was A. planoradiatus, 



