88 THE NAUTILUS. 



STUDIES IN NAJADES. 



BY DR. A. E. OUTMANN. 



The following studies intend to continue my " Notes upon the 

 families and genera of the Najades," published in the Annals of the 

 Carnegie Museum, vol. 8, 1912, pp. 222-365. They contain addi- 

 tional observations on the anatomy and systematic position of forms 

 which have come to hand since that paper was published. 



MARGAKITANA SINUATA (Lamarck). (See Ortmann, 1. c. p. 232). 



I have received from W. Israel the soft parts of two specimens 

 from the eastern Pyrenees, near Perpignan, France. 



The gill-structure of this species is entirely like that of M. marga- 

 ritifera, that is to say, the interlaminar connections are irregularly 

 scattered and do not form septa and water tubes, and near the base 

 of the gills there is a slight tendency to stand in oblique rows. The 

 jnner edge of the anal opening is almost smooth, with very slight and 

 indistinct crenulations, and does not differ from that of M. margariti- 

 fera. The connection of the posterior margins of the palpi extends, 

 in the two specimens before me, for a little less than one-half of the 

 margins, while in M. margaritifera they are connected for from one- 

 half to two-thirds, but this clearly depends upon the state of the con- 

 traction. 



MARGARITANA MARGARITIFERA (Linnaeus). (See : Ortmann, 1. c. 

 p. 220.) 



W. Israel sent me 10 gravid females of this species, collected 

 August G, 1912, in the Goernitzbach, Oelsnitz, Saxony. 



These specimens show that there is no difference whatever in the 

 shell of the two sexes, and chief of all, that the so-called " arcuate " 

 shape of the shell is not connected with sex. 



The structure of the gills, chiefly the arrangement of the interlam- 

 inar connections, is somewhat \ariable: the tendency of these con- 

 nections to form oblique rows is variously developed, and, as far as 

 I can see from the present material, is most strongly pronounced in 

 the female. However, I could not venture to warrant that it is pos- 

 sible to distinguish the sexes by this feature. 



In the gravid females, all four gills are charged : sometimes prac~ 

 tically the whole of the gills is filled with embryos ; in other cases a 



