NUCULA GIBBOSA. 179 



angles always pointing inwards, so that the anterior row is set in the opposite 

 direction to the posterior. 



The anterior adductor muscle-scar is situated at the anterior-inferior angle, 

 and is marginal, deep, especially above, and relatively large, marked off from the 

 rest of the shell by a ridge. The posterior adductor scar is not so deep as the 

 anterior, but its anterior border is also marked off by a ridge; it is marginal, 

 and situated at the junction of the hinge-line and posterior border. Anterior to 

 and above the latter, and close to the hinge-line, is a small punctate pedal 

 muscle-scar. The pallial line is obscure but entire. 



Exterior. — The valves are very thick compared with the size of the shell, and are 

 ornamented with numerous very fine concentric lines of growth, so fine that the 

 greater part of the surface is almost smooth. Towards the ventral border the 

 lines of growth become stronger, and irregularly interrupted by deeper sulci. 

 The valves were closed all round. 



Dimensions. — Fig. 4, PI. XIV, a specimen of average size, measures — 

 Antero-posteriorly . . . .19 mm. 



Dorso-ventrally . . . .11 mm. 



From side to side . . . .11 mm. 



Localities. — England : The Redesdale Ironstone, Northumberland ; Cougleton 

 Edge, Cheshire; Penton, Cumberland; in a bed of shale above the Gin Mine 

 Coal, Longton, North Staffordshire Coal-field. Scotland : Upper Limestone series 

 at Gare ; Robroystone ; in rock under George Square, Glasgow ; Orchard ; Waulk- 

 mill Glen, Thornliebank ; Swindridge ; and Linn Spout near Dairy. Middle Lime- 

 stone series : Bishopbriggs ; Lingula Ironstone, Carluke. Lower Limestone series : 

 above the Hosie Limestone, Campsie, and Thornton ; First and Second Kingshaw 

 and Calmy Limestones, Carluke ; High Blantyre ; East Kilbride ; Craigenglen ; 

 Auchenskeoech and Hindog Glen near Dairy ; Clonbeith, Kilwinning ; Daloch 

 Quarry, Fife ; East Barnes, Dunbar. 



Observations. — This shell is extremely common in those localities where it does 

 occur, and is to be obtained in all stages of growth. It was unmistakably 

 depicted by Ure, although the drawing is not equal to the work of modern 

 artists ; and John Gray refers the specimen preserved in the Ure Collection, now 

 in the Museum of the Royal Society of Scotland (antea, p. 17), to N. gibbosa. A 

 large number of specimens are present in collections from the original locality, and 

 the identity of the shell is thus placed beyond doubt. The specific name " gibbosa," 

 however, is due to Fleming, and dates 1828. Unfortunately Phillips did not 

 recognise this name, and applied the term " tumida " to the same species ; 

 and it was said to occur at " Bolland, Bowes, Northumberland ; Kulkeagh, 

 Ireland." Phillips's figure is typical of the species under discussion ; and so also 

 is his short description, " Gibbose, ovate, concentrically striated, beaks tumid." 



