152 



Dr. Gould observed, that shells in limestone waters 

 are less liable to erosion, not from any difference in their 

 composition, but simply because there is less tendency 

 in such waters to abstract lime from the shell. 



Prof. William B. Rogers suggested, that an analysis 

 of shells from various waters should be made, to deter- 

 mine any difference in their chemical composition. 



The Secretary read a letter from Dr. Samuel Kneeland 

 on a supposed new species of Siredon from Lake Supe- 

 rior. The following account was subsequently received : 



Siredon hyemalis, Kneeland. From 9 to 10 inches long ; 

 color on back olive-green, with a few small blackish spots, arranged 

 for the most part in longitudinal rows, and with a few smaller spots 

 varying in color from bright to rufous-yellow. A line, more dis- 

 tinct towards the tail, separating the olive-color of the back from 

 the sides, which are of a purplish-brown, with more numerous yel- 

 lowish spots sometimes coalescing into patches half an inch long and 

 two lines broad; brightest on sides of head and tail. Under sur- 

 face of body of an asby-brow^n color, with a more or less distinct 

 median white line, or linea alba ; the yellow spots occur on the 

 under surface of the jaw. From the nostrils, Avhich are situated 

 at the extreme corner of the truncated muzzle, about half an 

 inch wide, there I'uns a dark line through the centre of the eye 

 back to near the external gills; upper and lower segment of the 

 iris of a yellowish silvery color. Tail flattened laterally, ter- 

 minating in a rounded thin edge, more mottled than any other 

 part of the body. Gills, three in number on each side, exter- 

 nal, provided with an immense number of exceedingly delicate 

 fringes, of a deep red color when the animal is breathing ac- 

 tively ; these gills are kept waving to and fro in a most grace- 

 ful manner during active respiration ; when at rest they are 

 shrunken, still, and colorless. Just behind these gills are the 

 anterior extremities, about an inch in length, provided with four 

 fingers, mottled like the sides of the body; under suifnce of the 

 wrist and hand whitish, almost translucent, with the finger-tips 

 black. About five inches further back are the posterior extrera- 



