106 CATALOGUE OF 



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, subinaBquilateralis, orbiculato - ovalis, 

 ventricosa, tenuissime striata, nitida, valde fragilis : umbones 

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

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

 curvatum ad dimidium occultans ; 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 J the length of the shell, 

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

 with two flexures. 



11. 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. 



a. in. about ^ the length of a. /., 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. 

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

 arcuate, curving slightly towards the inner margin of 

 the hinge-plate. 



p. I. 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. in. about 3 the length of, and parallel to p. /., stout, 

 straight; apex central, scarcely prominent, obtuse 

 rounded; ridges rounded, descending about equally. 

 L.Y. a. n. 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. ii., apex somewhat backwardly directed. 

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

 anterior portion nearly parallel to shell - margin, 



