LBIOPTERIA HIRUNDO. ]:] 



naturally, or the size or stage of growth. The Avriter of the notes on L. M'Coi/i in 

 de Koninck's great work also thinks that M'Coy confounded two different species 

 under the title F. lasvigata, and refers the shell described last to L. M'Coi/i ; but I 

 am not prepared to say that the specimens figured by de Koninck as L. M'Coi/i 

 and L. lunulata are distinct. 



Avicula angusta, M'Coy, PI. IV, fig. 4, is a crushed and flattened specimen, which 

 from its shape must, I think, belong to L. lunulata. A. wfonnis is doubtless a 

 portion of the cast of the interior of a left valve of the same species. It is to be 

 noted that M'Coy's figure is very different indeed from that of the shell whicli is 

 labelled as the type. 



Leiopteeia HiErNDO, de Konind; 1885. Plate III, fig. 1. 



Leiopteria HIRUNDO, ch KoiiiiicJc, 1885. Ann. Mus. Roy. Hist. Nat. Belg., torn, 

 xi, p. 188, pi. XXX, figs. 1 and 2. 



Specific Characters. — Shell of medium size, obliquely convex, aviculoid. The 

 anterior end is well marked, triangular, compressed, separated from the rest of the 

 valve by a well-marked byssal groove. The antero-superior angle is a right angle, 

 the anterior border small and bluntly pointed. The inferior border desceruls 

 downwards and backwards in an almost straight line, but behind is l)luntly rounded 

 upwards to join the posterior margin, which is markedly falciform. The hiuge-liiie 

 is elongate and straight, produced backwards by a rolled rostrum. The umbones 

 are tumid and small, only slightly raised and placed far forwards, about one-fifth 

 the length of the hinge-line from the anterior end. The body of the valve is 

 obliquely tumid, but the swelling rapidly diminishes in amount as the valve 

 expands downwards and backwards. The posterior wing is comjjressed, triangular, 

 marked off from the tumid portion of the valve by a straight, oblique, shallow 

 sulcus, below which the gibbosity of the valve rises gradually. 



Interior. — Apparently normal. 



Exterior. — The surface is ornamented with numerous very regular, fine striae 

 and lines of growth, which are parallel to the contour of the margins. Shell very 

 thin. 



Dimensions. — PI. Ill, fig. 1, a specimen from the Carboniferous Limestone of 

 Castleton, measures — 



Antero-posteriorly . . . .40 mm. 



Dorso-ventrally . . . .28 mm. 



From side to side (estimated) . . .30 mm. 



Localities. — The Carboniferous Limestone of Ca.stleton, Derbyshire; Hill 

 Bolton, Yorkshire. 



