ortmann: south American naiades. 637 



My specimen, No. 5, from the Maranon is the one, which probably is injured, and 

 the length probably would be greater, when normal; this, of course, has influence on 

 the other indices, which are all somewhat too high. The figures taken from Sowerby 

 and Von Martens are close to mine. The greater height undoubtedly is due to 

 the larger size of the specimens, and probably also to the more anterior location of 

 the beaks. 



Anatomy. — Soft parts of one male and two females at hand, one of the latter 

 is gravid (collected February 6). 



The anatomy is that of the South American Mulelince, but it resembles that 

 of the African Mulelina', in having the anal opening closed above for about half 

 of its length. The opening is therefore comparatively short, being only a little 

 longer than the branchial opening, and reaching upward only to about the middle 

 of the adductor muscles. In other South American Mutelinai it reaches upward 

 beyond the posterior retractor-muscles. The anal is separated from the branchial 

 opening by a connection of the mantle; its inner edge is smooth. Branchial opening 

 with fine papilltp on the inner edge. Although Simi)son says that the branchial 

 opening is closed below, I cannot find any trace of a mantle-connection at the lower 

 (anterior) end. There is also no indication that such a connection has been torn 

 during life, or in preservation. Palpi long and low, their lower margins curved, 

 not drawn out into a posterior point, posteriorly with a short truncation, forming 

 the posterior margins, which are not connected. 



Foot very large, subcylindrical and subcompressed, at the distal end swollen 

 into a button-like knob. This structure is likewise not seen in other Muteline 

 shells. 



Ciills long and narrow, the inner the wider, the anterior ends as usual. Inner 

 lamina of inner gill entirely connected with abdominal sac. Distinct, continuous 

 septa of the Muteline type are present. The inner gill of the female is marsupial, 

 with thicker, but not more crowded, septa; the water-tubes are again divided bj' 

 vertical ridges into an inner and outer compartment, the inner of which serves as 

 ovisac, the outer as secondary water-canal. Eggs small, loosely hanging together. 

 I have not been able to find mature larvse in my gravid female. 



Genus Leila Gray (1840). 

 Simpson, 1914, p. 1399. 



The chief character of this genus is the sinus of the pallial line below the pos- 

 terior adductor-scar, which is said to be connected with the closing of the branchial 

 opening at its lower (anterior) end, but particulars about this arc not known. 



In other respects the shell of this genus is very similar to that of the species 



