357 



the Naiades into natural genera, from the structure of the ani- 

 mal as well as the shell, which had not been so well done before 

 from the shell alone. He proposed to include under one genus, 

 TJnio alatiis, TJ.fragilis^ U. gracilis^ U. Ohioensis, U. leptodon, 

 U. Sayii, U^ co7npressus, and U. rectus. Of Unio alatus he 

 remarked, that specimens from the western waters and from 

 Lake Champlain present differences in the teeth on the hinge 

 and in the general configuration of the shell, but. not in his 

 opinion enough to make a difference of species. U. gracilis 

 and TJ. fragilis, usually considered separate species, are only- 

 distinguished by similar differences. To another genus, Prof. 

 Agassiz proposed to refer U. perplexus and gihhosus, from char- 

 acters based on the more or less circumscribed disposition of the 

 essential internal organs. In conclusion. Prof. Agassiz said, 

 that the fact that the Unios are viviparous, though the young are 

 very small, and of extreme delicacy when excluded from the 

 mother, led to interesting speculations how it could have been 

 possible for so widely extended a family to have been distributed 

 by any influence not primitive. 



Prof. Wyman referred to a statement which he had 

 made at the meeting of October 16th, that the size of the 

 optic lobes is generally in relation to the power of vision. 



In the blind fish of the Mammoth Cave, Kentucky, there is an 

 apparent contradiction to this law, the optic lobes being quite 

 disproportionate to the rudimentary eye. In man, after long 

 bhndness, the lobe opposite the affected eye is found to be 

 atrophied. Prof. Wyman had recently had in his possession a 

 frog that had lost the sight of the right eye by the evacuation of 

 its humors. The eye was cicatrized, but he had no means of 

 knowing the age of the injury. On dissection the left optic lobe 

 was found one third less in size than the right. 



Mr. Desor called the attention of the Society to the 

 deposits of Marine shells in Maine, on Lake Champlain, 

 and the St. Lawrence, and to the question of their probable 



These deposits have been referred by geologists to the Ter- 



