6 THE NAUTILUS. 



On May 2nd I succeeded in securing a gravid specimen with 

 eggs and glochidia. All four gills were gravid, the inner con- 

 taining many more than the outer. Upon removing the mussel 

 from the water I at once placed a portion of the inner and outer 

 gills in preserving fluid. Even with this precaution, the initia- 

 tion of abortion was evident. The remainder of the mussel, 

 shell and soft parts, I wrapped in cloth, not having a container 

 large enough to fix at once. Upon arrival at the home station 

 I found that complete abortion of the contents of the marsupia 

 had taken place. 



Glochidia were present, somewhat immature, but Dnapping, 

 with a number of eggs presumably unfertilized. The glochidia 

 are sub-circular in form, i. e., circular except for the rather 

 short straight hinge line. Harms (1907-1909) figuring the 

 glochidia of M. margariti/era presents them somewhat pointed 

 and toothed. I can make out neither of these characters in M. 

 monodonta. The dimensions are: Height 0.055-0.065 mm., 

 length 0.055-0.0065 mm., thus being a little larger than those 

 reported for M. margariti/era and among the smallest of glo- 

 chidia. As the ovaries are well distended with eggs near 

 maturity I think there is no doubt that at least two broods are 

 produced in a season, as reported (Conner, Harms and Ort- 

 mann) * for M. margaritifera. 



I observed segmentation of ovarian eggs in this species in a 

 specimen which had been cut open and exposed to river water. 

 No data to my knowledge has been obtained relative to the 

 hosts for this species. 



Hemilastena ambigua : Nets placed near the mussel bed, for 

 the purpose of determining the host fishes of Q. heros yielded 

 some material that presented quite another problem. With the 

 fishes caught were a number of mud puppies, Necturus maculosus, 

 Rafinesque. From a total of fifteen caught twelve or 80 per 

 cent were infected with glochidia of mussels. Upon attempting 

 to identify these a few were found to be Q. heros not imbedded, 

 nor becoming so, after an attachment for a known period of 

 twenty-four hours and more. Evidently they were merely ac- 



1 See Ortmann, 1914. Annals Carnegie Museum, vol. 8, no. 2, 1912, p. 

 232. 



