SANGUINOLITES OBLONGUS. 397 



The umbones are small, depressed, compressed, and elongate, not raised above 

 the hinge-line, and placed near the anterior end of the shelh A well-marked 

 angular ridge passes obliquely downwards and backwards from the umbones to 

 the lower margin of tlie valve, terminating just in front of the postero-inferior 

 angle, and dividing the valve into two compressed triangular portions, the 

 lower and anterior being somewhat greater tlian the upper and posterior, which 

 forms the very broad and flattened dorsal slope, subdivided by two obscure 

 radiating lines. 



The lunule has not been observed. The escutcheon is long and narrow, and 

 elevated behind, where it is separated from the dorsal slope by an erect elongate 

 ridge. 



Interior. — The anterior adductor muscle-scar is large, shallow, and ovate, 

 situated immediately within the anterior margin rather low down. The posterior 

 adductor scar has not yet been exposed. Pallial line simple and remote from the 

 margin. The hinge-line has a rolled edge posteriorly. 



Exterior. — The surface is ornamented Avith numerous very fine concentric lines 

 and strise of growth, somewhat interrupted on the dorsal slope by two radiating- 

 lines. Shell thin. 



Dimensions. — PI. LXIII, fig. 7, in the collection of the Geological Survey 

 Museum, Jermyn Street, measures — 



Antero-posteriorly . . . .98 mm. 



Dorso-ventrally . . . .45 mm. 



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



Localities. — England : the Carboniferous Limestone of Park Hill and Castle- 

 ton, Derbyshire, and Bolland, Yorkshire. Ireland : the Carboniferous Limestone 

 of Millicent, co. Cork. 



Observations. — I have founded this species on five specimens, two of which are 

 in the Museum of the Geological Survey, Jermyn Street ; two in the Woodwardian 

 Museum, Cambridge; and one very fine example is in the Gilbertson Collection of 

 the British Museum (Nat. Hist.). S. ohlovrjus belongs to the tricostatiis group, 

 having the dorsal fold subdivided by two or three radiating striae ; but in general 

 shape, and in the marked angularity of the ridge, it differs widely from 

 8. tricostatus, Portlock, sp. In two of the specimens the oblique ridge is much 

 accentuated by crushing, and curiously both these examples are from Ireland, one 

 example being in the Woodwardian, the other in the Jermyn Street Museum. 



The paucity of specimens is to be regretted, and especially the absence of shells 

 in the earlier stages of growth. Indeed, it has occurred to me that these shells 

 may possibly be a giant form of S. tricostatus, whose comparative dimensions have 

 been changed by excessive growth. 8. tricostatus is mostly more gibbose, has 

 a more acute ridge, the posterior end is the deepest part of the shell in a dorso- 



