100 THE NAUTILUS. 



delphia, Ark., who is actively engaged in developing the fauna of 

 Arkansas. The generic name is an abbreviation of the name of its 

 native state. 



THE ANATOMY OF THE NAJAD HYRIDELLA AUSTEALIS (LAMAECK) 

 ( = DIPLODON AUSTEALIS). 



BY A. E. ORTMANN. 



Through the courtesy of Mr. L. S. Frierson, I have received the 

 soft parts of a male and a femaUi of an Australian Najad, Diplodon 

 {Hyridelhi) australis (Lamarck) (see Simpson, Pr. U. S. Mus. 22, 

 1900, p. 890). Mr. Frierson obtained these specimens from Mr. 

 William T. Bednall, who collected them in Gippsland, Victoria. I 

 also received a shell which agrees well with specimens of this species 

 represented in the Carnegie Museum collections. An examination 

 of the soft parts revealed the following characters: 



Anal opening (a) closed above by the connection of the inner 

 mantle edges, without forming a supraanal opening. Closed part 

 about four times as long as the anal o^emn^^ forming a rather broad 

 memhrane between the outer mantle edges, and around the anal. The 

 latter is short, subcircular or sliglitly subelliptic, and much shorter 

 than the branchial opening (only about one-fourth as long). It is 

 separated from the bi'anchial opening by the solid union of the inner 

 mantle edges (m). Inner edge of anal practically smooth, that of 

 the branchial (b) with distinct papillae, which stop suddenly in 

 front, thuG defining sharply the anterior end of this opening. There 

 is no sign of a coalescence of the two mantle halves at this point. 

 Farther in front, the inner mantle edge is smooth, and becomes in- 

 distinct anteriorly. 



Palpi subtriangular, about as long as wide, with the posterior 

 point not produced. Posterior margins connected about half their 

 length. 



Gills rather long and wide, the inner the wider, chiefly so an- 

 teriorly. Edge of inner gill with a longitudinal furrow, which is 

 absent in the outer gill. Outer gill gradually narrower anteriorly, 

 with its anterior end situated at the highest part of the mantle- 

 attachment-line. Inner gill very slightly narrower anteriorly, with 

 a broad anterior insertion occupying the whole space between the 



