THE NAUTILUS. 



129 



& Pidg., which had been communicated to him by Mr. L. P. 

 Gratacap of the American Museum, New York. They are 

 from Wladiwostok, southeast Siberia. Both had glochidia, 

 which proved to be similar to those of TJnio. 



The examination of these specimens has established the 

 following facts: All of the features of the family Unionida 

 (1. c, p. 223) are present. The diaphragm is complete, and 

 formed only by the gills (no mantle connection between anal 

 and branchial openings), and the outer lamina of the outer 

 gills is connected with the mantle to its posterior end. The 

 anterior end of the inner gills is separated from the palpi by 

 a gap. A supraanal opening is separated from the anal by a 

 mantle connection. The gills possess continuous septa, form- 

 ing water tubes running parallel to the gill filaments. 



The characters of the family Unionwue (1. c, p. 224) are 

 also present. The marsupium is formed by the outer gills, 

 and, when charged, these gills swell only moderately, leaving 

 the edge sharp. There are no secondary water tubes. 



For the rest, it should be said that the mantle connection 

 between anal and supraanal openings is moderately long, 

 about half as long as either. The anal has the inner edge 

 distinctly crenulated; the branchial opening has distinct 

 papillae; but in front of the branchial the mantle edge is 

 smooth. Palpi subfalciform, their posterior margins united 

 for about one-third of their length. 



GUIs rather long and narrow, the inner the wider, chiefly 

 anteriorly; their anterior ends as usual. Inner lamina of 

 inner gills free from abdominal sac posteriorly, but connected 

 anteriorly ; in one of my specimens the connection extends to 

 one-third of the length of the abdominal sac, in the other to 

 nearly one-half of it: thus this character is variable, as in 

 certain other forms of Nayades (Haas says only: connected 

 anteriorly). 



Septa and water tubes well developed in the outer gills of 

 the female, this character extending all along the gill. Pla- 

 centa present, but not very solid, the glochidia easily falling 

 apart. Glochidia essentially agreeing with those of Unio 

 [type, pictorum (L.) ; see Ortmann, Naut., 28, '14, pp. 32, 



