J2 SMITHSONIAN INSTITUTION 



Ohio Canal below Sycamore Island. Those from Occoquan Creek, 

 above the fall line, are without spiral sculpture and usually olive green, 

 sometimes with a spiral band of brown. They duplicate Goniobasis 

 of the Shenandoah River (see the top row of fig. 74). The specimens 

 taken at Dawsons Beach are all spirally lirate, that is, they have uni- 

 form spiral threads (see the bottom row of fig. 74). The specimens 

 taken from the Chesapeake and Ohio Canal are not of uniform size, 

 coloration, or sculpture, but vary enormously in all three of these 

 characters, as shown in the middle row of figure 74. These are be- 

 lieved to be hybrids of the mollusks above the fall line of the Atlantic 

 coast, that is, the smooth form and the spirally lirate form of the 

 mouth of rivers just above the influence of salt water, while the inter- 

 mediate forms, like those about Washington, I believe to be the product 

 of crossing of the other two, i. e., mutations produced by hybridiza- 

 tion, a fact to be proved or disproved by the experiment. 



In one of the Millville cages we placed 500 tips of the year from 

 Dawsons Beach, in another 500 of the complex occurring at Wash- 

 ington, and in the third 500 each of tips taken above the fall line of 

 Occoquan Creek and Dawsons Beach. 



In the Roaches Run Bird Sanctuary we placed 500 tips of the year 

 from Dawsons Beach in one cage, in another 500 tips taken from 

 Occoquan Creek above the fall line, while in a third we placed 500 

 each from these two localities. 



At Fort Belvoir we shifted our cages from the Fisheries Station 

 to the pontoon station where they will be less subjected to shifting 

 ice this winter, and here we placed 500 tips of the year taken above 

 the fall line in Occoquan Creek, in another cage 500 of the Washing- 

 ton complex, and in the third 500 each of the Occoquan and Dawsons 

 Beach specimens. 



Although we consider that the experiments of the past 2 years are 

 largely negative, as far as Goniobasis is concerned, they nevertheless 

 presented some interesting facts in other directions. For example : 

 In the mud in the cages at Roaches Run and Fort Belvoir we found 

 specimens of the mollusk Anodonta cataracta Say, one of which mea- 

 sured 66.2 mm in length, 40.0 mm high and a diameter of 19.3 mm ; 

 the glochidium from which this was grown must have been shed by 

 fish upon the cage and fallen through the wire mesh and developed to 

 this size in 8 months. Some of these Anodontas bear as many as 

 eight " annulations ", which in the past have been considered indica- 

 tions of annual increments ; in other words, the shell in question, 

 which must have been no older than 8 months, would in the past have 

 been said to be 8 years of age. 



