SPECIES OF PISIDltTJI. 117 



uhique sulcato-striata, marginibus omnibus regulariter arcu- 

 atis, parte posteriore brevissima, unteriore duplo longiore, 

 ad murgines comprcssa, sed obtusissima ; umbones validi, lati, 

 tumido-rotundati, prominentes." 



No details were given concerning the hinge characters, which, 

 may be thus particularized: 



Hinge (PI. II, f. 9 ; IV, f. 5) about f the length of the shell, 

 narrow, scarcely projecting save at the urnbo, not very strong, 

 flatly arcuate. 



R.V. a. /. about ^ the length of the hinge-line, narrow, not very 

 strong, strongly bowed inwards ; base fairly strong, 

 somewhat swollen ; apex central, prominent, pointed 

 obtuse ; ridges somewhat rounded, sloping about 

 equally, at first steeply and then running out 

 horizontally. 



a. in. about 4 the length of a. /., from which it is separated 

 by a deep fossa, not very strong or prominent; apex 

 about central, not very prominent, somewhat out- 

 wardly inclined, rounded obtuse ; ridges sloping away 

 about equally. 

 5. lamellit'orm, prominent, nearly straight, top irregular; 



b somewhat thickened, sometimes sulcate. 

 p. i. about | the length of the hinge-line, narrow, fairly 

 strong, straight, erect ; base fairly strong and swollen ; 

 apex distal side of centre, prominent, somewhat 

 acuminate; ridges fairly sharp, umbonal descending 

 fairly steeply at first, then gradually, distal very 

 steep. 



p. in. about ^ the length of p. /., from which it is separated 

 by a deep fossa, very inconspicuous, closely apposed to 

 the shell-wall; apex very obtuse. 



L.Y. rt. li. about | the length of the hinge-line, rather narrow, 

 strong, straight ; base strong, somewhat swollen ; apex 

 central, exceedingly prominent, acuminate, somewhat 

 distally directed, with peculiar outward twist ; ridges 

 sharp, distal sloping down very steeply and descending 

 to a lower level than the umbonal, which is not quite 

 so steep. 

 2. very prominent, obtusely triangular, with backwardly 



directed apex, base coiitinuous with that of a. n. 

 4. lamelliform, not prominent, nearly straight, running 

 backwards from above 2 with slight downward diagonal 

 inclination. 



p. u. about | the length of the hinge-line, rather narrow, 

 strong, straight ; base strong, slightly swollen ; apex 

 near distal end, very prominent, acuminate ; ridges 

 sharp, descending about equally, very steeply at first 

 and then gradually. 



