132 



N. ot. = Otocyst nerve. 



N. p. = Pedal nerves. 



N. pa. = Ant. pallial nerve. 



N. pall. = Visceral pallial nerve. 



N. pp. = Post, pallial nerve. 



0. = Ova. 



0' = Young ovinu. 



Op. F. = Ophthal. pallial fold. 



Op. m. = Eye stalk muscles. 



Op. n. = Optic nerve. 



Op. n. i. = Inner branch ditto. 



Op. n. o. = Onter branch ditto. 



Ot. = Otocyst. 



P. = Periostracmn. 



P. b. = Byssal groove. 



P. gr. = Periostracal groove. 



P. M. r. = Radial pall, muscles. 



P. s. = Periostracal glands. 



Per. = Pericardium. 



Pig. = Pigment cells. 



R. = Rods of retina. 



R. G. = Rod-cells ditto. 



R. C. n. = Nuclei, rod cells. 



E. C. p. = Pseudo-rod cells. 



Ro. = Renal organ. 



Ro. c. = Gland, epith. ditto. 



Ro. c'. = Ditto, Avith concretions. 



Ro. con. = Connect, tissue, renal org. 



Ro. ep. = Epithel., renal org. 



Ro. m. = Intrinsic muscles, renal org. 



Ro. rp. ■= Reno-reprod. apert. 



Ro. V. = Renal veins. 



S. = Spermatozoa. 



S. D. = Dors, venous sinus. 



8. m. i. = Basement membrane. 



S. m. 0. = Sieve membrane. 



iS' V. r. = R. vent, venous sinus. 



Scl. = Sclerotica. 



Sep. = Septum. 



Sh. a. = Auricula of shell. 



Sh. F. = Shell fold, mantle. 



Sh. m. = Calcar. layer of add. im]iress. 



Sh. p. = Artie, surf, of shell. 



T. = Tapetum. 

 Tn. = Tentacle. 



Tn. V. = Velar tentacle. 

 Til. m. = Tunica muscularis. 

 Tu. p. = Tunica propria. 



V. = Velum. 



V. a. = Adductor veins. 



V h. = Hepatic vein. 



V. M. = Radial velar muscles. 



V. M. a. = Attach, of velar muse. 



F. M. c. = Concent, velar muse 



V. p. = Pedal vein. 



V. pall. = Pallial vein. 



V. V. = Visceral veins. 



Yen. = Ventricle. 



Plate I. 



Fig. A. P. opereularis, right valve, showing byssal 

 notch. Natural size. 



B. F. oj^ercularis, left valve. Natural size. 



C. P. inaximus, exterior 11. valve (young), x |. 



D. P. maximus, exterior L. valve (young). x f . 



E. P. inaximus, interior of \i. valve, showing 



adductor impression and pallial line (slightly 

 darkened), also ligament and ridges of hinge 

 area. x |. 

 Fig. F. P. maximus, interior of L. valve; pigmented 

 specimen showing muscular impressions, x j. 



Fig. 

 Fig. 

 Fig. 



