Howard. — Restricted Parasitism in Mussels 43 



species, is parasitic upon a single genera of fishes far 

 removed genetically from the hosts of the others. 



My experiment will illustrate how a study of natural 

 infections was of assistance. The gar would not have 

 been included in this test ordinarily, as it is commonly 

 thrown away as a nuisance. I had found it infected with 

 glochidia which I identified with some uncertainty as L. 

 anodontoides. On this account when the opportunity 

 came to infect with the yellow sand shell I made a special 

 effort to bring in the gars with the other fishes. 



The natural infections which I collected first on July 

 17, 1912, were upon the long-nosed gar (Lepisosteus 

 osseus Linn.). 



The following year infected gills of the alligator gar, 

 (L. tristoechus Bl. and Schn.), were sent to the labora- 

 tory from Indiana by Mr. Ernest Danglade. These were 

 identified as the glochidia of the yellow sand shell. As I 

 used the short-nosed gar (L. platostomus) in my experi- 

 ments, we have a pretty clear indication that any of the 

 three species of gar is a suitable carrier for this mussel. 



Definite results in a similar manner were obtained with 

 the Missouri niggerhead (Obovaria ellipsis Lea). Natural 

 infections of doubtful identification had been found on 

 the sturgeon (Scaphirhynchus platorhynchus Raf.). This 

 was an especially difficult case because the infections in 

 question were of an appearance and dimensions corre- 

 sponding to those of a group of glochidia which are much 

 alike, viz. : Lampsillis ventricosa Bar., L. fallaciosa Simp., 

 L. higginsii Lea., Obovaria ellipsis Lea., and Quadrula 

 pustula Lea. In the experiments the glochidia of O. ellipsis 

 remained and passed through the parasitic stage on the 

 sturgeon while they were promptly shed by the black 

 bass, sunfish (Lepomis pallidus) , sheepshead (A. grun- 

 niens) , white crappie, black crappie, and channel catfish. 

 It will be noted that the sturgeon did not retain glochidia 

 in the other experiments. 



The butterfly shell (Plagiola securis Lea.) I have found 

 in several instances of natural infection on the sheeps- 

 head (A. grunniens) . In artificial infections I obtained 



