1!J18.] Ekendkajvahi Giio.sii : Anutonty of U niunidae. 121 



(6) The 'non-(jlandular portion passes forwards beneath the peri- 

 cardial chamber. The relation of the non-glandular to the glandular sac 

 has already been described. At the anterior end, the non-glandular 

 sac is separated from its fellow by the vertical portion of the rectum. 

 The excretory aperture is placed at the outer ventro-lateral aspect of 

 the sac. The interrenal aperture is elongated in Laniellidens and Hole- 

 naia, but is less so in Physunio. 



IX. Reproductive System. 



The gonads are placed as usual amongst the coils of the intestine and 

 a porticju of the rectum in the visceral mass. In Lamellidens manjinalis 

 male specimens were available. The head of the spermatozoon is 

 rod-shaped, about thrice as long as broad, rounded anteriorly, truncate 

 or slightly concave, and widest posteriorly ; there is a slight constriction 

 in the middle. The tail is very fine and is about 3 or 4 times as long as 

 the head. 



X. Nervous System. 



The position of the ganglia is practically the same as that in Ano- 

 donta. The ganglia and the connectives could not be dissected out in 

 Solenaia. 



The cerehro-jjleural (janglion of each side gives oft" (1) an inter cerebral 

 connective in front of the mouth, (2) a pallial nerve from the antero- 

 lateral aspect, (3) a cerebro-visceral commissure and (4) a cerehro-yedal 

 commissure. No other nerve was found arising directly from the cerebro- 

 pleural ganglion. 



The pedal ganglion, on each side, gives oft 6 nerves from, the side and 

 receives the cerebro-pleural commissure. The otocyst lies inside the 

 pedal ganglion. 



The visceral ganglion, on each side, receives the cerebro-visceral 

 commissure and gives oft' 3 nerves, a branchial, a })osterior pallial nerve, 

 and a small nerve to the posterior adductor muscle. 



In Lamellidens the branchial nerve passes along the conjoined margin 

 of the inner lamella of the outer and the outer lamella of the inner gill. 

 It divides into two branches, one passing along the same margin and the 

 (jther along the fused margins of the inner lamellae of the inner gills. 

 The posterior pallial nerve divides into 3 branches : — (1) a small nerve 

 to the mantle-lobe which passes to the attached margin of the outer 

 lamella of the outer gill, a little in front of its posterior end ; (2) a 

 nerve to the mantle-lobe at the posterior end of the attached outer 

 lamella of the outer gill ; (3) a nerve to that portion of the mantle-lobe 

 which forms the lateral wall of the cloacal chamber. 



The cerebro-visceral commissures are placed side by side between the 

 two glandular portions of the kidneys beneath the vena cava in Lamelli- 

 dens. They are separated from one another by the lower end of the 

 vena cava in Physunio. 



SUMMARY. 



The anatomy of the three genera of llnionidae dealt with in this 

 paper agrees in general structure with that of Anodonta and Unio as 



