98 CARBONIFEROUS LAMBLLIBRANCHIATA. 



rounded. The binge-line straight and comparatively short. The umbones 

 gibbose, pointed, incurved, almost central. The anterior ears larger than the 

 posterior ears, well defined, compressed-triangular, with margin rounded ; the 

 posterior ears narrow but deep and compressed. 



Interior. — Unknown. 



Exterior. — The surface of both valves is ornamented by several unequal, 

 flattened, broad, radiating ribs, the majority of which pass from umbo to margin. 

 Every second or fourth rib is more prominent and larger than the others. The 

 ribs are crossed by fine crenulate lines visible under the microscope, and one speci- 

 men shows six radiating colour-bands, the strong ribs dividing the bands and 

 apparently being free from colour. The anterior ear has unequal radiating ribs 

 crossed by concentric strias of growth. 



Dimensions. — PL XVII, fig. 26, from Castleton, Derbyshire, measures — 

 Antero-posteriorly . . . .2(3 mm. 



Dorso-ventrally . . . .21 mm. 



Localities — England : the Carboniferous Limestone of Castleton, Derbyshire. 

 Ireland : the Carboniferous Limestone of Little Island, co. Cork ; Caherass, co. 

 Limerick; St. Doulaghs, co. Dublin. 



Observations. — I have founded this species on several specimens, two from the 

 collection of Mr. Joseph Wright, of Belfast, and three in my own. Mr. Wright 

 has appended the MS. name of GarroJll in honour of his friend Mr. Isaac Carroll, 

 the botanist; and I have been glad to adopt it. Thespecies is easily identified by 

 the irregular flattened ribs. It has the same general shape as A. Murchisoni. I 

 have, I think, identified correctly as a right valve a specimen in the Geological 

 Survey Collection, Dublin. It has very similar marking to the left valve. The 

 Derbyshire specimen has colour-bands and every fourth rib large, but does not 

 show the crenulations on the ribs, which are present in the Irish examples, and 

 the latter show every second rib to be enlarged. Since writing this description 

 and arranging the plates, some much larger examples have occurred to me from 

 St. Doulaghs. 



Avici lopecten Murchisoni, M'Coy, sp., 1844. Plate XIV, figs. 3 — 7. 



Pecten Murchisoni, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 97, pi. xviii, 



fig. 3. 

 — ovatus, M'Coy, 1844. Ibid., p. 97, pi. xiv, fig. 11. 

 Avictjlopecten Muechisoni, de Koninch, 1885. Ann. Mus. Roy. d'Hist. Nat. 



Belg., torn, xi, p. 21i), pi. xxxvi, fig. 21. 



Specific Characters. — Shell below medium size, triangularly ovate. The left 

 vulve convex, the righl flattened. The anterior margin almost straight, oblique. 



