458 



MEMOIRS OF THE CARNEGIE MUSEUM. 



2. Marsiipiuin (Fig. 3, i) with well-developed, continuous septa, forming well- 

 defined, isolated water-tubes, with a peculiar longitudinal ridge or swelling on the 

 septa near the outer lamina of the gill (PI. XLVIII, figs. G, 8). When gravid, 

 only the inner compartment of the water-tubes (towards the inner lamina) is some- 

 what extended and filled with eggs; the outer compartment becomes a secondary 

 water-tube (PI. XLVIII, fig. 76). 



3. Non-marsupial gills (Fig. 3, o) also with septa and water-tubes, but the 

 septa less strongly developed and without a ridge. 



4. Inner lamina of inner gills entirely 

 connected with abdominal sac (South Ameri- 

 can forms), or free from it (African forms). 



5. Palpi nearly semicircular, longer than 

 high, with a short posterior truncation, 

 strongly curved lower margins, and indis- 

 tinct posterior points (Fig. 3, h). 



6. Larva supposed to be a lasidium 

 (according to Von Ihering). 



The shell generally has no beak-sculp - 

 tiu'e whatever. In veiy rare cases a trace 

 of concentric sculpture has been observed 

 (see under Anodontites trapezea). Hinge- 

 teeth more or less obsolete, reduced in nimi- 

 ber, or size, and very often entirely absent (Anodontine type of hinge). Dorsal 

 muscle-scars mostly absent in South American forms, very rarely a faint trace 

 seen, or a few are present, as in Leila. In African forms, there is one single well- 

 developed dorsal muscle-scar. 



Fig. 3. Diagram of soft parts of female of 

 AnodontUes patagonica rubinmda (Lea). Nat- 

 ural size, left section of mantle removed, a, 

 Anal opening; 6, Branchial opening; h, Palpi; 

 i, Inner gill; o, Outer gill; p, Pes; t, Union of 

 mantle separating anal and branchial openings. 



Subfamily HYRIIN.E Ortmann. 

 General Remarks. 



Shell of various shapes, subelliptical, subtrapezoidal, subovate, suborbicular, 

 or subtriangular, sometimes more or less alate. Beak-sculpture mostly present, 

 rarely missing, but often indistinct or obliterated by erosion, always of the radial 

 type, with two sets of radial ridges, starting from two points, immediately in front 

 and immediately behind the tip of the luiibo, and extending to a varying degree 

 upon the disk. The posterior ridges of the anterior set, and the anterior ridges of 

 the posterior set, generally interfere with each other in the middle of the disk, 



