THE NAUTILUS. 107 



The shell of my specimen has nothing remarkable, and there is no 

 sculpture visible near the beaks. 



According to the above observations there is no question that both 

 Parreysia and Lamellidens group with my subfamily Unionina, but 

 that they differ generically from the North American forms. The 

 investigation of more Asiatic types is very desirable. 



AFRICAN FORM. 



Spatha kamerunensis Walker. In NAUTILUS, August 24, '10, p. 

 39, I have given the description of the soft parts of this species. 

 The chief differences from the North American, and also from the 

 Asiatic, forms are the following (see pi. VI, fig. 5, and pi. VII, fig. 5): 



1. The inner gill decreases very little in width in front, and is 

 attached in its whole width to the whole length of the ascending part 

 of the mantle-attachment line, and thus its anterior end comes in 

 contact with the posterior end of the palpi. 1 



2. The palpi are broad and short, with a very insignificant point 

 behind, and not at all falcate; their posterior margins are not 

 connected. 



3. The anal and branchial openings are sharply separated by a 

 bridge, formed by the firm union of the mantle edges, which extends 

 somewhat inward, and thus 



4. The diaphragm is formed posteriorly by this bridge, and not 

 by the gills, which do not reach the posterior mantle margin. 



5. The anal opening is closed above by the union of the inner 

 mantle edges without leaving a supnuinal opening.* 



6. The septa of the well developed water tubes are rather remote 

 from each other and strong. 



7. In the female, the inner gills alone are used as marsupium, the 

 septa becoming wider, but not closer set (this structure practically 

 occupies the whole gill). 



Larvae were not found in the specimens at hand. 



These differences, pre-eminently 1, 3, 4, and 7, are fundamental, 



1 The inner lamina of the inner gill is free from the abdominal sac. Accord- 

 to von Ihering (Zool. Anz. 14, '91, p. 479, and 15, '92, p. 2) it should be 

 connected. 



'The anal opening is continued upward, above the rectum, as a supraanal 

 canal, which ends blindly. 



