160 CARBONIFEROUS LAME LLIBRANCHI ATA. 



The valve is hollowed by a broad shallow compression from hinge-line to lower 

 margin, anterior to the umbo, elsewhere it is very gently and evenly convex. 



Interior. — The posterior adductor muscle-scar is almost obsolete, placed in 

 the hollow of the dorsal slope, high up and remote from the posterior end. The 

 hinge-plate of the right valve contains a large, thick, prominent, cardinal tooth, 

 immediately posterior to and beneath the umbo, obliquely twisted. 



Exterior. — The surface is smooth in front where concentric lines of growth are 

 seen on the anterior portion, elsewhere ornamented by numerous, flattened, 

 radiating ribs, which become almost obsolete at the extreme posterior end. The 

 ribs are separated by shallow sulci, and bifurcate as they cross the valve. 



Observation*. — This genus has been established on a number of specimens, the 

 majority of which were obtained from the Carboniferous Limestone of Little 

 Island, co. Cork. I find these shells have generally been referred to Avicula 

 flabellula, M'Coy, but whatever that species may be, it possessed ears and a short 

 hinge-line, and has the characters of Pseudamusium. 



It is not easy to make out the affinities of this species, or, indeed, to determine 

 the correct orientation of the shell. I have described the short smooth end as 

 anterior, but am not at all certain that this is correct. A specimen from 

 Auchenmade (Plate XXIV, fig. 13), which I feel sure belongs to the same genus, 

 though the species is perhaps distinct, shows a strong cardinal tooth in the right 

 valve. This forbids any reference to Pectinidse or Aviculidas, and also to 

 Solenomyidse. 



The anterior end appears to be thin and gaping. Dr. Kitchin and Mr. E. A. 

 Smith have kindly looked at my specimens and have both stated that the shells 

 are quite unlike any hitherto described, and they are unable to suggest their 

 systematic position. 



Nothamusium radiatum, sp. nov. Plate XXIV, figs. 9 — 11. 



Specific Characters. — The generic description has been drawn up from this 

 species, with the exception that the hinge-plate has not been observed. It 

 therefore need not be repeated here. 



Dimensions. — Plate XXIV, fig. 11, measures — 



Antero-posteriorly . . . .31 mm. 



Dorso-ventrally . . . .21 mm. 



Convexity of valve . . . .3 mm. 



Localities. — England: the Carboniferous Limestone of Narrowdale, Stafford- 

 shire. Ireland : the Carboniferous Limestone of Little Island, Co. Cork. 



