60 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 



narrowed by a convergence of the dorsal and ventral margins. Inferior border 

 uniformly and convexly curved, or there may be a concave sinuation in it 

 posteriorly. 



Umbones situated in the anterior one-third of the shell raised above the rest 

 of the shell, tumid and very blunt, widely separated in casts and excavated 

 internally in front, so that they appear to have an oblique direction forwards and 

 outwards. Lunule wide, rapidly widening anteriorly, marked by longitudinal stria?, 

 which are continuous with lines of growth of the shell. In those specimens which 

 have a sinuated ventral margin an almost obsolete, shallow, broad, oblique 

 constriction is seen on the side of the shell, commencing near the umbones, it 

 passes downwards and backwards, gradually widening until it terminates in the 

 sinuated portion of the inferior border. 



Valves somewhat convexly flattened ; greatest convexity is situated immediately 

 below the umbones. Posterior slope bluntly rounded or angulated. Hinge-line 

 straight in casts, and there is no indication of any anterior or lateral cardinal teeth. 

 In right valve there is a single obliquely diverging tooth, with a pit posterior to 

 it to receive the corresponding tooth of left valve. 



Shell moderately thick, marked with concentric stria? and very fine lines of 

 growth. 



Plate VII, fig. 8, measures — 



Antero-posteriorly . . . .38 mm. 



Dorso-ventrally . . . .22 mm. 



Laterally . . . . .15 mm. 



Localities. — Low Moor, Bradford ; Thin bed, Burnley. 



Observations. — I have been permitted to refigure the original shells of Sowerby's 

 figures of Unio subconstricta (PI. VII, figs. 5 — 7) by the kindness of Dr. H. 

 Woodward. The feature of the shallow oblique sinus is not at all uncommon in 

 many other species of Garbonicola, and can no longer be regarded as a specific 

 character. As a matter of fact, it is much shallower in the form under description 

 than obtains in many specimens of G. acuta and G. robusta ; indeed, M'Coy (op. cit., 

 p. 515) thought that C. robusta was only an adult form of G. subconstricta. 



I know of only two specimens which retain the shell, and these are in the 

 " Sowerby Collection" (British Museum). There is also a fine series of casts in 

 the Woodwardian Museum at Cambridge, which nevertheless show very faint 

 striae over the lower part of the shell (figs. 8 — 10, PI. VII). 



The form of G. subconstricta appears to me to connect G. acuta with G. aquilina, 

 there being a marked approach towards the shape of the anterior end of G. sub- 

 constricta and C. aquilina ; and there is also to be noted in the former a slight 

 degree of obliquity to the long axis of the shell in the lines of growth. 



M'Coy laid great stress upon the presence of an obtuse angle along the dorsal 



