119 



Taking color, therefore, as a sufficient ground for specific distinc- 

 tion, we find that we have in. the red-tailed group seven species, and 

 in the other nine, which, with the young Harlani of the Academy, 

 Cooperi, fuliginosus, albonotatus, lineatus, elegans, and Pennsylvani- 

 cus, give a total of twenty-three species of this genus which are found 

 in the United States. {See table on page 118.) 



Mr. C. Stodder read the following paper : — 



Organisms found in the Mud from the bottom of Mystic 

 Pond, Medford, near Boston. By R. C. Greenleaf and 

 Charles Stodder. 



Some of the mud from the bottom of Mystic Pond, obtained by the 

 soundings of the officers of the United States Coast Survey, having 

 been presented to Mr. Greenleaf, he, with myself, have examined it 

 for the organisms which might be found in it. This is a fresh-water 

 lake, the source of Mystic River, in Medford, about seven miles from 

 Boston. The surface of the lake is about the level of ordinary high 

 tides ; it has a narrow, shallow outlet. Extreme high tides flow into 

 the pond. The pond being something like seventy feet deep, the salt 

 water flowing in with the tide, sinks to the bottom, and cannot escape. 

 Consequently, the water at the bottom is constantly salt, while the 

 surface water is usually fresh. This singular lake, might be expected 

 to afford evidence of both lacustrine and marine life, and such proves 

 to be the case. In the natural state of the mud we find the exuviae of 

 minute crustaceans. On cleaning it by levigation and the application 

 of acids, we find spicules of sponges ; also, one species of the dictyoca 

 of Ehrenberg, and one of periptera, the origin of which are unknown, 

 though classed by Ehrenberg among the Polygastric infusoria. Many 

 small fragments of shells of Polycistinae, — too imperfect to identify 

 the genera, — and also a gi-eat variety of shells of the diatomacea, 

 both marine and fresh water. Among which we identify the fol- 

 lowing species : — 



