THE NAUTILUS. 107 



shape, color of inside (rose color), and sculpture of outside. 

 Frierson, who has seen these shells, also thinks that they belong 

 to this species. 



Simpson (Descript. Catal., 1914, p. 1013) makes this a syn- 

 onym of U. rusticus Lea (1856), and places it in the genus 

 Nodularia. But Lea's shell is larger, heavier, has more ele- 

 vated beaks, and coarser and more obscure sculpture. This is 

 also evident from the figures of rusticus given by Haas (Syst. 

 Conch. Cab. 9. Heft 44, 1911, pi. 21, f. 2-5 , where the spe- 

 cies is placed in the genus Contradens Haas. 



Haas (1. c. Heft 48, 1913, p. 173) defines this genus by the 

 sculpture of the shell, and chiefly by the character of the hinge 

 teeth, and describes the anatomy of two species (C. hageni 

 Strub. and verbecki Bttgr. ), which agrees fully with that of the 

 European Unio. However, the glochidia are peculiar in not 

 having a spinulose, triangular hook, but a swelling of the lower 

 margin covered with fine spinules arranged in vertical rows. 

 (This undoubtedly is a primitive structure, which, in its further 

 development, leads to the hook of Uiiio and of the Anodontinae). 

 Of the septa, Haas says that they are u well developed." 



Anatomy of my specimens of Contradens cambojensis: 



Anal opening separated from the supraanal opening by a 

 moderate mantle connection ; supraanal very short, anal with 

 inner edge nearly smooth ; branchial opening with papillae on 

 inner edge. Anal and branchial openings separated by a gill- 

 diaphragm, of the normal Unionid-type. No special structures 

 on mantle edge in front of the branchial opening. Palpi sub- 

 falciform, large, their posterior margins united for two-thirds or 

 almost three-fourths of their length. 



Structure of gills Unionine, but in the male and in the inner 

 gill of the female, the septa are extremely weak and scarce, 

 almost absent. 



The outer gill of the female is marsupial in its whole length, and 

 when charged, moderately swollen, with sharp edge. Septa are 

 present, and stand close, forming water tubes, but the septa are 

 incomplete, interrupted, so that the water-tubes (ovisacs) commu- 

 nicate with each other. In the charged and distended mar- 

 supium, the septa practically are replaced by rows of somewhat 



