552 MEMOIRS OF THE CARNEGIE MUSEUM. 



New Localities. — Rio Uruguay (in mud), Urugaayana, Rio Grande do Sul, 

 Brazil (J. D. Haseman coll., February 5, 1909). One young male with soft 

 parts. Rio de la Plata, Han Isidro, 20 km. north of Buenos Aires, Argentina (A. 

 Windhausen coll., January 1917). One male with soft parts. 



Distribution. — From the La Plata near Buenos Aires up to the Rio Parana and 

 Rio Paraguay in Paraguay', and also in the Rio Uruguay. 



The descriptions given by D'Orbigny, Von Ihering, and Simpson agree well 

 with our specimens, but it should be mentioned that the beak-sculpture sometimes 

 covers less than half of the adult shell. The hinge-teeth are very variable, but 

 Von Ihering's account represents the normal condition. The laterals are said 

 to be smooth or finely smoothly striated. In my young specimen they have dis- 

 tinct, vertical, irregular, and granular ridges; in my larger specimen they are ir- 

 regularly granular and crenulated, but have no distinct vertical ridges. 



According to Von Ihering, the maximum length is 70 mm. ; according to D'Or- 

 bigny, 75 mm. The height according to the former is 77 to 80 pr. ct.; according to 

 the latter, 76 pr. ct.; the diameter is 50 and 49 pr. ct. respectively. The beaks are 

 located, according to Von Ihering at 17 to 23 pr. ct. of the length. 



Thus our larger specimen is unusually swollen. 



Remarks. — This species somewhat resembles the genus Castalia, chiefly on 

 account of the strong development of the beak-sculpture. However, according to 

 the posterior slope, which is distinctly elevated along the upper posterior margin, 

 and also according to the structure of the lateral teeth, which have the vertical 

 ridges poorly, or not at all, developed, it is a Castalina. In Castalia furthermore the 

 diameter of the shell generally is much greater than the maximum (60 pr. ct.) ob- 

 served in the present species. 



Anatomy. — Soft parts of two males at hand. Color whitish. 



Anal opening slit-like, closed above; closed part three to four times as long as 

 the open, the latter shorter than the branchial opening, and separated from it by 

 a solid mantle-connection. Branchial with small papillae. In the smaller siDCcimen, 

 the branchial opening is closed in front by a firm union of the mantle-margins, 

 but in the larger specimen there is no such connection, and thus in this species 

 this character is variable. Palpi rather large, nearly subfalciform, with the lower 



