who 

 col- 

 his 



P 



made of wire netting and attached to a long handle, jointed like a fish- 

 pole. This net was of great value in securing specimens which were 

 beyond the reach of the arm and in bringing up those species which 

 live on a muddy bottom in rather deep water. Professor Parker had 

 provided a two-quart pail for the purpose of carrying home some of the 

 living snails and clams. 



We prepared for our first collecting at a point in the lake where the 

 shore was sandy and gradually sloped into deep water. The bottom was 



thickly dotted with little pro- 

 jections sticking out of the 

 sand and mud. Harry, 

 was our most energetic 

 lector, having removed 

 shoes and stockings, and hav- 

 ing rolled up his trousers, 

 waded into the water, and 

 brought to us a handful of 

 these objects which proved to 

 be fresh-water clams, or Unios, 

 like those pictured in the ac- 

 companying figure. 



The shells were a rich, yel- 



7 \J 



lowish green color, with rays 

 of dark green extending from 

 the umbones to the ventral 

 margin. Some of the speci- 

 mens were beautifully polished, 

 while others were covered with a hard incrustation of mud at one end. 

 Howard, who was a beginner, and knew little about mollusks, asked 

 what the shell was made of and how it opened. 



As we were all a little tired by our walk over the swampy ground 

 near the lake, we sat down upon a grassy bank while Professor Parker, 

 in answer to Howard's question, gave the following talk on clams: 



"In the clams, oysters, and mussels, the shell is composed of two 

 convex pieces, or valves (hence called bivalves), which are generally 

 on each side of the animal and are attached to each other at the dorsal 

 or upper margin by a tough, elastic, horny ligament. In the oysters and 

 some other shells the two valves are not side by side, but are upper and 

 lower ; but of these we shall learn more at another time. 



" The rounded, raised portion of the shell at the upper part of each 

 valve is called the beak, or umbo (plural umbones), which is marked by 



2 



Fresh-water clam, showing different parts of 

 shell. Upper figure, right valve exterior; lower 

 figure, both valves viewed from above; A, anterior 

 end; P, posterior end; D, dorsal margin; V, ven- 

 tral margin; R, right valve; L, left valve; 1, liga- 

 ment ; Ig, lines of growth ; lu, lunule; u, umbo. 



