106 CATALOGUE OP 



Still, it may have been overlooked on account of its small size. 

 If found it will probably, judging from its build, prove an inhabitant 

 of quick-running rather than stagnant water, and should be looked 

 for in fine sand rather than mud. 



The original diagnosis (179, p. 553) reads : 



" Concha minima, subinsequilateralis, orbiculato - ovalis, 

 ventricosa, tenuissime striata, nitida, valde fragilis : umbones 

 prominentes, acutiusculi : dentes card. valv. sinistrae 2, tenuis- 

 simi, exterior brevis, interiorem brevem, paullo crassiorem, vis 

 curvatum ad diraidium occultaus ; dens card. valv. dextra? 

 tenuis, vix arcuatus, parte posteriore paullulum incrassatus." 



The above description does not give the hinge characters 

 sufficiently in extenso and may be supplemented as under : 



Hinge (PI. II, f. 6 ; IV, f. 8) about | the length of the shell, 

 very broad and strong, projecting well inwards, highly arched, 

 with two flexures. 



ll.V. a. i. about 3 the length of the hinge-line, very stout and 

 strong, curving somewhat inwards ; base very strong 

 and swollen ; apex central, not very prominent, 

 rounded obtuse, inwardly directed ; ridges rounded, 

 sloping about equally and fairly steeply, the umbonal 

 descending somewhat the lower. 



0.7/7. about 1 the length of a.i., from which it is separated 

 by a deep pit, stout, straight, closely apposed to the 

 shell-margin ; apex central, scarcely prominent, very 

 rounded obtuse; ridges rounded, sloping about equally. 

 3. short, lamelliform, very prominent, flat-topped, slightly 

 arcuate, curving slightly towards the inner margin of 

 the hinge -plate. 



p. 7. about 4 the length of the hinge-line, narrow, strong, 

 erect, straight ; base very strong and swollen ; apex 

 distal side of centre, scarcely prominent, somewhat 

 obtuse, pointed ; ridges sharp, umbonal descending 

 fairly steeply to the lower level than the distal which 

 is less steep. 



p. ni. about g the length of, and parallel to p. /., stout, 

 straight ; apex central, scarcely prominent, obtuse 

 rounded; ridges rounded, descending about equally. 

 L.Y. a. 77. about 3 the length of the hinge-line, stout, strong, 

 straight ; base very strong and swollen ; apex central, 

 very prominent, pointed, obtuse; ridges sharp, distal 

 descending very steeply at first and then gradually, 

 umbonal fairly steeply. 

 2. triangular, prominent, base continuous with that of 



a. //., apex somewhat backwardly directed. 

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

 anterior portion nearly parallel to shell - margin, 



