THE NAUTILUS. 17 



NOTES ON THE GLOCHIDIA OF STROPHITUS EDSNTULUS PAVONIUS 



(LEA) FROM COLORADO. 



BY M. M. ELLIS AND MARIE KEIM. 



While collecting material for class use from St. Vrain Creek, 

 near Longmont, Colorado, December 6, 1817, 25 specimens of 

 Strophitus edentulus pavonius (Lea) (det. J. Henderson) 

 were obtained. Of these, 15 contained large numbers of well- 

 developed glochidia. These glochidia soon freed themselves 

 from the cords when the cords were placed in water after 

 being removed from the gills of the parent mussels, and each 

 individual glochidium began active snapping movements. 

 Many individuals lived for two or three days after leaving 

 the cords and continued active all the while. 



This record of gravid specimens of Strophitus edentulus 

 pavonius is later in the year than any record given by Surber 

 (Bur. Fish. Doc. 771, 1912) for Strophitus edentulus from the 

 Mississippi River, November being the last month in which he 

 found glochidia-bearing individuals of that species. 



When compared with the figures and description given by 

 Surber (1. c.) for Strophitus edentulus, the glochidia of these 

 Colorado mussels of the variety pavonius were found to differ 

 in both size and proportion from the Strophitus edentulus 

 type. As these differences may have some taxonomic signifi- 

 cance, occurring as they do in the glochidia of a variety of 

 Strophitus edentulus taken near the western edge of the range 

 of that variety, the following description of the glochidium of 

 Strophitus edentulus pavonium is given. 



General shape that of the Anodonta type as given by Surber 

 (1. c.) but of a form intermediate between that of Strophitus 

 edentulus (fig. 3, 1. c.) and that of Anodonta grandis (fig. 45, 

 1. c.) ; hinge line straight; depth slightly greater than the 

 length; marginal spines three, well developed, the median 

 spine being slightly longer than the two lateral spines; from 

 seven to ten rows of spines, counting the marginal row, on 

 each valve ; end of the adductor muscle showing from 35 to 

 50 distinct bundles of fibers. The exact measurements of 20 

 specimens are given below. 



