SPKCIMS OF I'JSIDll'M. 127 



17. Pisidium vincentianum, n. sp. 



(Pis. 11, f. 2 ; IV, f. ; XXVII, f. 7-11.) 



Testa parva, ovato-subtrigona, satis inaequiliteralis, ventricosa, 

 teuuissime striata, rugis increment! elevatis hie illic 4-5 praedita : 

 superne rotundato-cunica, uiubonibiis prominentibus, obtusissimis ; 

 autice prolongato-rotnndata ; postice truncato-rotundata ; inferne 

 arcuata. Cardine tenui, dentibus validis ; ligameuti fossa brevis, 

 maxime depressa, fere ad inurum testae apposita. 



The detailed hinge characters are : 



Hinge (PI. II, f. 2 ; IV, f. 6) about f the length of the shell, fairly 

 wide, projecting somewhat inwards, and very strong, exceedingly 

 arcuate, interrupted at ligament-pit which recedes back against 

 the shell- wall. 



11. V. . /. about | the length of the hinge-line, narrow, strong, 

 faintly curved inwards ; base very strong and swollen ; 

 apex distal side of centre, not very prominent, obtuse- 

 pointed ; ridges fairly sharp, descending about equally 

 and fairly steeply at first, then gradually. 

 a. in. at out | the length of a./., to which it is parallel, narrow, 

 straight, somewhat inclined against the shell-wall ; 

 apex near distal end, not very prominent, very obtuse ; 

 ridges sharp, sloping about equally. 



8. very prominent, sickle- shaped, the rounded end, 6, 

 sulcate and overhanging the inner margin of the hinge- 

 plate. 



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

 straight ; base strong, somewhat swollen ; apex central, 

 moderately prominent, obtuse-pointed; ridges fairly 

 sharp, sloping about equally and fairly steeply. 

 p. 777. about 3 the length of p. /., to which it is parallel, narrow, 

 not very strong, straight, somewhat inclined against the 

 shell-wall ; apex obtuse-pointed ; ridges sharp, sloping 

 about equally and fairly steeply. 



L. V. a. 77. about | the length of the hinge-line, very narrow, strong, 

 straight ; base very strong and swollen ; apex on dibtal 

 side of centre, very prominent, obtusely acuminate ; 

 ridges sharp, sloping about equally and very steeply. 



2. prominent, obtusely triangular, apex backwardly directed 

 and pointing towards the umbo, base continuous with 

 that of a. 77. 



Jf. lamelliform, sharp, prominent, seeming to spring from 

 the shell-margin under the umbo, and curving gently 

 backwards round 2 to about half across the hinge- 

 plate. 



p. ii. about | the length of the hinge-line, very narrow, strong, 

 straight ; base strong, swollen ; apex central, very pro- 

 minent, obtusely acuminate ; ridgfs sharp, umbonal 



