SPECIES OF risnmM. 



denfcibos cardinalibus rainimia, srepe subnullis lateralibus 

 compressis, vix prominulis, ligainento brevi, minimo." 



The further description of the hinge-characters necessary to 

 pplement the above is as follows : 



Hinge (PI. II, f. 10 ; IV, f. 3) about f the length of the shell, 

 fairly strong, narrow, especially the middle third under the umbo, 

 projecting slightly inwards, slightly curved, with two flexures. 



K.V. a. i. about | the length of the hinge-line, narrow, strong, 

 slightly bowed inwards; base strong, straight; apex 

 near distal end, prominent, bluntly obtuse ; ridges 

 fairly sharp, about equally steep, the umbonal de- 

 scending about twice as low as the distal. 

 a. in. about J the length of, and parallel to a. /., straight, 

 narrow, outwardly inclined ; apex central, very obtuse- 

 pointed ; ridges sharp and descending equally and 

 gradually. 



3. lamelliform, sharp, not very prominent, flat-topped, 

 faintly arcuate, parallel with the shell-margin. 



p. i. about I the length of the hinge-line, very narrow, 

 strong, faintly bowed inwards ; base fairly strong, 

 shelving down into the shell-wall ; apex near distal 

 end, not very prominent, pointed, obtuse ; ridges some- 

 what rounded, umbonal descending gradually to a 

 lower level than the distal which is somewhat steeper. 

 p. in. about i the length of, and parallel to p. 7., narrow, 

 somewhat outwardly inclined ; apex distal side of 

 centre, not very prominent; ridges sloping fairly 

 gradually and equally. 



L.V. a. ir. about | the length of the hinge-line, fairly narrow, 

 slightly bowed inwards ; base strong, shelving down 

 into the shell-wall ; apex distal side of centre, very 

 prominent and acuminate ; ridges sharp, distal de- 

 scending very steeply at first and then gradually, 

 umbonal very steeply to a lower level than the distal. 

 2. prominent, very obtusely triangular, parallel with 

 hinge-margin ; apex outwardly directed. 



4. lamelliform, sharp, slightly arcuate, curving round 

 and parallel to the apex of 2. 



p. n, about \ the length of the hinge-line, narrow, strong, 

 slightly inwardly bowed ; base strong, shelving down 

 into shell-wall ; apex near distal end, very prominent, 

 acuminate ; ridges sharp, umboual sloping gradually, 

 distal very steeply. 



Dimensions. Held's specimens must have been very small, for 

 his measurements converted into millimetres are : Long. 1-8, 

 Alt. 1-6, Crass. 1-5 mm. Baudon gives 2'5 or 3x2-5 or 3x2-5 

 and Clessin 3-2 x 2'5 x 2'3 mm., but a specimen from Cemmaes Bay 

 (Anglesey) is 3-6x3x2-7 and one in Mr. Oldham's collection 

 from Dean Row, VVilmslow (Cheshire), attains 3'75x 3x2-25 mm. 



