SANGUINOLITES ARGUTUS. 369 



CucuLL^A ABGUTA, Etheridge, 1888. Brit. Foss., pt. 1, Palaeozoic, p. 282. 



Pakallelodon aegutus, Jnlien, 1896. Carbonifere marin de la France centrale,. 



p. 48. 



Macrodus aegutus, Tornquisi, 1896. Fossilfuhr. Untercarbon. Sudvoj;;esei], ii, 



Abb. genl. Karte Elsass-Lotbr., vol. v, 

 p. 104, pi. xix, fig. 31. 



Specific Characters. — Shell below medium size, very inequilateral, transversely 

 ovate, gibbose, strongly carinate, narrowed in front and behind. The anterior 

 end is small, narrowed, gradually compressed into the margins; and its border is 

 rounded, the lower part being the arc of a much larger circle than the upper. 

 The lower border is slightly but regularl}'' convex, and meets the posterior border 

 at a blunted acute angle. The posterior margin is short, straight, obliquely 

 truncate from above downwards and backwards, joining the hinge-line above at a 

 very obtuse angle. The hinge-line is long, slightly arched in front, but straight 

 and depressed posteriorly. The nmbones are small, pointed, incurved, tumid, 

 somewhat raised, and placed in the anterior quarter of the shell. Passing down- 

 wards and backwards from the umbo obliquely to the postero-inferior angle is a 

 sharp narrow ridge, which separates the convex part of the valve from the dorsal 

 slope. The latter is so much and so rapidly compressed as to be markedly 

 concave from side to side. The concave slope is narrow close to the umbo, but 

 becomes broader as it descends, and is limited internally by an acute line which 

 separates it from the elongated escutcheon. Passing from the umbo to the 

 posterior border halfway across this slope is an obscure radiating groove. 

 Lunule well developed. 



Interior. — Quite unknown. 



Exterior. — The surface is ornamented with well-marked concentric ribs, 

 which are crowded and bifurcated at times in front, or have others introduced 

 between them; towards the lower margin of the valve they may interdigitate. 

 These ribs cease abruptly along the oblique ridge, and are represented on the 

 dorsal slope by close-set fine lines, passing directly upwards to terminate in the 

 iipper border. 



Dimensions. — I have met with no perfect example, but the dimensions of the 

 type of Phillips's Ciicidlsea arguta (PI. XL, fig. 15) are — 



Antero-posteriorly . . .19 mm, (estimated) 



Dorso-ventrally . . . .10 mm. 



From side to side . . . .8 mm. 



Localities. — England : the Carboniferous Limestone of Bolland, Yorkshire, 

 and Thorpe Cloud, Derbyshire. 



Observations. — The type specimen of Phillips's CucuUsea arguta is preserved in 

 the Gilbertson Collection in the British Museum (Natural History), Cromwell 



48 



