SPECIES OK risiDirir. 



127 



17. Fisidium vincentianum, n. sp. 

 (Pis. II, f. 2; IV, f. 6 ; XX VII, f. 7-11.) 



Testa parva, ovato-subtrigona, satis iuaequiluteralis, ventricoea, 

 icnuissime striata, nigis increment! elevatis hie illic 4-5 piaedita : 

 superue rotundato-conica, umbonibus pronuinentibus, obtusissimis ; 

 autice prolongato-rotundata ; postice truncato-rotundata ; inferno 

 arcuata. Cardine tenui, deutibus validis ; ligameiiti fossa brevis, 

 maxitne depressa, fere ad murum testae apposita. 



The detailed hinge characters are : 



Hinge (PI. II, f. 2 ; IV, f. 6) about | 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. ///. at out | the length of ./., to which it is parallel, narrow, 

 straight, somewhat inclined against the shell-wall ; 

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

 ridijes sharp, sloping about equally. 



3. very prominent, sickle shaped, the rounded end, &, 

 sulcate and overhanging the inner margin of the hinge- 

 plate. 



p. I, 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. in. 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. . //. about | the length of the hinge-line, very narrow, strong, 

 straight ; base very strong and swollen ; apex on dis-tul 

 side of centre, very prominent, obtusely acuminate ; 

 ridges sharp, sloping about equally and very steeply. 

 2. prominent, obtusely triangular, apex back \vardly directed 

 and pointing towards the umbo, base continuous with 

 that of . //. 



4. 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. ir. about | the length of the hinge-line, very narrow, strong, 

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

 minent, obtusely acuminate ; rid yes sharp, umbonal 



