18 



THE NAUTILUS. 



Length in micro, 



254 

 256 

 258 

 260 

 260 

 260 

 260 

 260 

 260 

 260 



The modal average of the specimens examined gives an aver- 

 age length of about 260 and an average depth of about 270, 

 the range of variation being 254 to 272 for the length and 260 

 to 280 for the depth. Surber (p. 8, 1. c.) states that the 

 length is greater than the depth in Strophitus edentulus and 

 gives 350 for the length and 285 for the depth as average 

 measurements. 



The behavior of the living glochidia was interesting in the 

 light of the work of Lefevre and Curtis (Bur. Fish. Doc. 756, 

 1912) on the metamorphosis of Strophitus edentulus without 

 parasitism. These writers state (p. 173) that they were un- 

 able to bring about the attachment of the glochidia to fish. 

 Our glochidia of Strophitus edentulus pavonius were offered 

 gills from the Topminnow, Fundulus zebrinis Jordan & Gil- 

 bert and of the Sunfish Lepomis cyanellus Rafinesque (these 

 two species of fishes are found in St. Vrain Creek) imme- 

 diately after the gills were removed from the body of the fish. 

 Fish blood caused an evident increase in the activity of the 

 glochidia and several glochidia seized gill filaments. Once 

 attached the glochidia remained on the gill filament until the 

 experiment was discontinued, i. e. for several hours. No 

 attempt to infect living fish with the glochidia of Strophitus 

 edentulus pavonius was made, but the behavior of the living 

 glochidia suggests physiological differences between the glo- 

 chidia of Strophitus: edentulus and these western specimens 

 of Strophitus edentulus pavonius. 



University of Colorado, May, 1918. 



