16 THE NAUTILUS. 



Cotype No. 2, width, 14 mm. ; height, 11 mm. Univ. Colo. 

 Mus. 



Cotype No. 3, width, 12.8 mm.; height, 10.6 mm. Univ. 

 Colo. Mus. 



Cotype No. 4, width, 13 mm. ; height, 10.8 mm. Univ. Colo. 

 Mus. 



Cotype No. 5, width, 13.5 mm. ; height, 12 mm. Univ. Colo. 

 Mus. 



Cotype No. 6, width, 14 mm. ; height, 10.8 mm. A. N. S. 

 Phila. 



No. 5 is a melanistic example with no light band. 



GLOCHIDIA IN SURFACE TOW1NGS. 



BY H. W. CLARK AND SAMUEL STEIN. 



In their article on "Reproduction and Parasitism in the 

 Unionidfe," by LeFevre and Curtis (Journ. of Experimental 

 Zoology, Vol. IX, No. 1, p. 98), under the caption, "Behavior 

 and Reactions of Glochidia," occurs the following statement: 



"At the time of spawning the glochidia, already free from 

 the egg-membranes and more or less loosely held together in 

 slimy strings, are discharged at irregular intervals through 

 the exhalent siphon. Being heavier than water, they sink 

 rapidly to the bottom, coming to rest with the outer surface 

 of the shell directed downward and the valves gaping widely 

 apart." The belief was formerly general that they "swim" 

 about by rapidly opening and closing the valves, after the 

 manner of Pecten, and in spite of frequent denials by Schier- 

 holz ('88), Latter ('91) and others, the same statement is 

 still occasionally encountered. In the recent volume on Mol- 

 lusca in the Treatise on Zoology, edited by Lankester, this 

 inexcusable error is represented. "The glochidia," we are 

 again informed, "swim actively by clapping together the 

 valves of the shell" (p. 250). They are, on the contrary, as 

 is now well known, entirely incapable of locomotion and re- 

 main in the spot where they happen to fall, and that "The 



