29 



shell exhibits two stages of growth ; the first in color and appear- 

 ance much like the canal shell, and equivalent to the adult shell 

 found in the canal ; the second stage of growth, separated from 

 the first by a very distinct varix or cicatrix, is of a lighter color, 

 usually of an ochraceous yellow, the surface of the shell check- 

 ered or broken up into irregular facets, evidently the result of the 

 rapid growth of the animal, by which the shell was too rapidly 

 enlarged, to be evenly solidified. The " old lock " shell is a less 

 solid shell than the other. 



Dr. Lewis's communication was accompanied by the fol- 

 lowing note from Mr. T. J. Whittemore. 



Gray " is of opinion that the calcareous rim within the peri- 

 stome of certain Lymnsese and Planorbes, is formed when the 

 waters they inhabit are nearly dried up ; or in winter, when they 

 are affected hy cold, preparatory to their secretion of a dia- 

 phragm for their protection at these times," (see Haldeman's work 

 on Lymniades,) and this was distinguishable in a variety of L. 

 fragilis, marked D in Jiis work, L. 7, Plate 6 ; and he further 

 says " that the varieties D and E have the minute spiral lines, 

 very distinctly marked, but the irregular reticulations are want- 

 ing ; when these are present, the surface is divided into a series 

 of facets, which have been compared to those upon cut glass." 



The remarks of Dr. Lewis are very interesting, particularly in 

 regard to the growth and change in appearance of the Lymncea 

 catascopiimi, and appear by the shells to indicate that the two 

 neighboring localities produce the same shell, although so differ- 

 ent in appearance ; yet the old growth has the same appearance. 



Mr. Bouve called the attention of the Society to some 

 points of interest in the Collection of Ornithichnites, recently 

 purchased for the Society, deferring a more elaborate report 

 to a future meeting. He remarked that the largest and 

 most valuable slabs were then in the room, and of these he 

 called attention to one upon which the impressions of rain 

 drops were very numerous and distinct. Another, of coarser 

 sandstone and of lighter color, exhibited rain drops in relief. 



