CONOCARDIUM ROSTRATUM. 455 



the subcylindrical anterior portion, which often appears as if twisted on itself 

 owing to the external markings. Posterior to the ridge the valve is still more 

 rapidly compressed and narrowed from below upwards, becomiog continuous with 

 the long, narrow, tubular rostrum, which projects backwards from the upper part 

 of the posterior border, and which is only a little shorter than the anterior end. 

 At the line where the striated portion of the valve passes into the anterior 

 cylindrical part is an almost obsolete oblique sinus. 

 Interior unknown. 



Exterior. — Tlie body of the shell is covered with close, regular, radiating ribs 

 and sulci, more apparent in worn or decorticated specimens; but in fine examples 

 only fine concentric striae and lines of growth may be apparent. In front the 

 ribbed portion of the shell becomes smooth ; but further forwards very fine 

 oblique strijB, often mere rows of elongated tubercles, pass very obliquely over the 

 upper edge of the valve and proceed downwards and forwards to the anterior end. 

 Posterior to the ridge the ribs are larger and wider apart, and fewer in number, 

 but they become obsolete as they pass into the rostrum. 



Dimensions. — PI. LI, fig. 7, a specimen from Park Hill, in the Museum of the 

 Greological Survey of England and Wales, Jermyn Street, measures — 



Antero-posteriorly, from anterior end to tip of rostrum . 26 mm. 



Length of rostrum . . . . 8'5 mm. 



Dorso-ventrally . . . . . 6 mm. 



From side to side . . . .8 mm. (estimated). 



Localities. — England : the Carboniferous Limestone of Settle and Bolland 

 (Phillips), Yorkshire; Bakewell and Park Hill, Derbyshire; Wetton and Narrow- 

 dale, Staffordshire. Scotland : the Lower Limestone series of Auchenmade ; 

 Law quarry, Dairy, and Langside, Beith, Ayrshire ; Potmetal plantation. Bogie, 

 Kirkcaldy. 



Observations. — A specimen of this species without the rostrum was the 

 original of Martin's Gonchyliolithiis (Arcites) rostratus, considered by him to belong 

 to Area. This species was re-described and figured by Sowerby {op. cit.), but 

 unfortunately he substituted the name elongatus, of which Arcites rostratus, Martin, 

 is said to be a synonym. Sowerby's specimen, also without the rostrum and 

 incomplete in front, was presented by Martin, and may have been the original, 

 though Sowerby states that the specimen was presented to him before Martin 

 began his work. The original of Sowerby's figure is preserved in the Sowerby 

 Collection in the British Museum (Natural History), and I am permitted to 

 refigure the shell by the kindness of the authorities, PI. LI, fig. 6. Phillips 

 re-described the species, adopting Sowerby's name, so that, till de Koninck in 1842 

 restored Martin's name, the shell was known from Sowerby's rather than from 

 Martin's figure. 



