Manchester Memoirs, Vol. xli. (1897), No. 0. 



3 



conoidal. Apex halfway between centre and posterior 

 margin. Surface covered with equidistant concentric 

 lines of growth. Ventral valve flat, more circular than 

 free valve, and bearing a narrow slit-like foramen passing 

 from the centre to the posterior margin. Marked with 

 concentric striae as in the free valve. Shell thin and 

 horny. 



Diameter 13 mm. 



Localities and Horizons: Carre Heys, Colne ; roof of 

 Bullion coal, low r er coal-measures. 



Ashton Moss Colliery, Ashton-under-Lyne ; "Marine- 

 band," middle coal-measures. 



Observations .- This form has been known for a long 

 time from the Lancashire coal-measures. It is a much 

 less robust species than Discina nitida, and less elevated. 

 It approximates somewhat to Discina Davreuxiana, but is 

 flatter, smaller, and more circular. The dorsal valve of 

 D. orbicularis is extremely low, almost flat. 



Aviculopecten Cairnsii, sp. uov. (PL 5, f. 3 and 4). 



Diagnosis : Valves feebly convex, wider than long, 

 inequilateral and markedly oblique. Surface bearing faint 

 concentric striations, probably lines of growth. Hinge 

 line straight, short, and about half the length of the shell. 

 Anterior ear of right valve small, and gradually merging 

 into anterior border. Posterior ear marked with four or 

 five strong rounded ribs ; byssal notch deep. Ears of 

 left valve equal, and concentrically striated. 



Locality and Horizon : River Tame, Dukinfield ; " Marine- 

 band," middle coal-measures. 



Observations : This species is a little larger than A . 

 Jibrillosus, Salter, with which it is found in association, 

 and presents important differences. It is a much more 

 oblique form, and destitute of the radiating ribs which 

 are so conspicuous a feature in Salter's species. The 



