56 CARBONIFEROUS LAMELLIBRANCHIATA. 



number, which pass from the umbo to the margin, becoming broader as they 

 approach the free edge of the valve, and separated from each other by shallow 

 grooves, in which secondary ribs may arise, these being intercalated between the 

 primary ones. The ribs show small tumefactions at intervals in their course. The 

 ribs are coarser and wider apart towards each extremity. Concentric lines of 

 growth are seen crossing the valves at irregular intervals. 



Dimensions. — PL IX, fig. 14, measures — 



Antero-posteriorly . . . .50 mm. 



Dorso-ventrally . . . .40 mm. 



Convexity of valve (left) . . .3*5 mm. 



Localities. — England : the Carboniferous Limestone (upper beds) of Settle, 

 Yorkshire ; Castleton, Park Hill, and Thorpe Cloud, Derbyshire. Ireland : 

 Carboniferous Limestone of- St. Doulagh's, co. Dublin ; Little Island, co. Cork ; 

 Kildare. 



Observations. — The type of Phillips's Avicula radio ta is a very small shell, and 

 it is not difficult to understand why the species has not been recognised by 

 authors. The type specimen (PI. IX, fig. 16) is preserved in the Gilbertson 

 Collection, Natural History Museum, South Kensington, and is a very young 

 stage of growth of the left valve. An examination of any of the larger examples 

 and a study of the contour of a young example by comparing the lines of growth, 

 sIioav that Phillips's shell has exactly the same contour as the young stage of 

 de Koninck's Aviculopeden Bosquetianus. I am therefore compelled, on the 

 grounds of priority, to retain Phillips's name instead of that given by de Koninck. 

 I have seen specimens of the right valve, which is very flat, but have met with 

 none which were sufficiently well preserved to be figured. This species has been 

 described and figured under the name of A. Bosquetianus on two occasions by 

 de Koninck, who obtained his specimens from Vise. Although de Koninck stated 

 that this species occurred in Bolland, it has not been inserted in any British list 

 of fossils from the Carboniferous Limestone so far as I can ascertain. Referring 

 to this species in a foot-note, de Koninck alludes to the essential identity of the 

 shell with the Devonian species referred by Hall to Pterinopecten, but he hesitates 

 to accept any subdivision of the genus Aviculopeden. 



Pterinopecten radiatus resembles P. papyraceus more closely than any other 

 shell, but the nodular character of the ribs and the more transverse shape form an 

 important and easily recognised difference between the two species. PI. IX, fig. 13, 

 represents a peculiar variety of P. radiatus, in which the ribs are few and wide 

 apart, due to the fact that only in very few places have intercalating or secondary 

 libs been formed. Another peculiarity in this specimen is the well-defined anterior 

 ear separated from the body of the valve by a deep groove. It belongs possibly 

 to another species, but 1 hesitate to describe a new species from a single specimen. 



