490 MEMOIRS OF THE CARNEGIE MUSEUM. 



Bartsch has given a description of the soft parts of huapensis, which refers 

 chiefly to the general features, the color, the structure of the siphons, and the 

 shape of the gills and ijalpi. But no particulars as to the structure of the gills are 

 given. 



Anal opening slit-like, closed above, closed part about four times as long as 

 the open, the latter with the inner edge smooth, and separated from the branchial 

 b.y a solid mantle-connection. Branchial opening with distinct papillae. Palpi 

 of moderate size, subtriangular, lower margins curved, posterior margins not 

 connected at base. 



Gills nearly of the same width posteriorly, the inner much wider than the 

 outer anteriorly. Outer gill subtriangular, its anterior end at the highest point 

 of the mantle-attachmcnt-line. Inner gill with gently convex margin, very little 

 narrower anteriorly, broadly attached in front, its anterior end immediately be- 

 hind the palpi. Inner lamina of inner gill entirely connected with abdominal sac. 

 Interlaminar connections of non-marsupial gills weakly developed, scattered. 

 Marsupiwn located in the inner gill, but not occupying all of it, leaving nearly 

 one-fifth of the gill free anteriorly, and about two-fifths posteriorly, so that the 

 marsupium is distinctly shifted forward, Ijnng in the second and third fifth of the 

 gill (from the anterior end). Interlaminar connections of the marsupium forming 

 interrupted septa, the septiform structure apparently prevailing (this is not quite 

 clear, since the structure is obscured by the masses of glochidia). The charged 

 marsupium is a little swollen, and the glochidia fill it in a loose mass, not being 

 conglutinated. 



Glochidium subtriangular, strongly oblique, with the point of the lower margin 

 located vertically below the posterior end of the hinge-line. Hooks are present 

 and of the normal S-shape. L. 0.25, H. 0.20; L. of hooks: 0.05 mm. Compared 

 with other species, the glochidium is rather small. 



2. Species from coastal streams of southern Brazil. 



It is a noteworthy fact that species of the chilciisis-type seem to be absent 

 from the system of the Rio de la Plata (with the exception of the drainage of the 

 upper Parana). They also seem to be absent in the great Amazons-basin, and 

 northward. But they are found rather plentifully on the Brazilian plateau, be- 

 ginning at its southern extremity, in the coastal streams in Rio Grande do Sul, 

 going thence northward, and crossing over in Sao Paulo and Parana into the drain- 

 age of the upper Parana River. 



We shall take up first the species of the coastal streams, and I wish to call 



