LETTERS FROM PROF. AGASSIZ. 183 



Cambridge, June 15, 1853. 

 My Dear Sir: 



On my return to Cambridge, a fortnight ago, 

 after an absence of more than six months, I was delighted 

 to find a memorandum from you, and the very interesting 

 specimens of young Unio, (Crassus,) you have had the 

 kindness to send to me. 



There can be no doubt that the b3^3sus which protrudes 

 from these shells is of the same nature as that of our com- 

 mon Muscle, Mytilus edulus, and other species that attach 

 themselves. It is an important link more between the 

 different families of Bivalves, and shows again how many 

 features, which seem to differ in the adults, may be found 

 to agree between the young. This fact at once assigns a 

 higher position, in their respective families, to the species 

 that have no byssus over those that are provided with it. 



Though I have been dangerously sick for two months 

 last Winter, I have spent a very interesting time at the 

 South and West this Spring. I collected over sixty new 

 species of fishes, mostly from the rivers emptying into the 

 Gulf. I have also paid particular attention to the genus 

 Lepidosteus, of which I have obtained several new species. 



It is so long since I have heard from you directly, that I 

 am doubtful whether you received my two last letters, one 

 written from Cambridge, about a year ago, the other from 

 Charleston last March, and that I can hardly venture upon 

 trespassing upon your time to request you again to let me 

 have that collection of fishes from Lake Erie and your 

 Rivers, which you so liberally offered to me spontaneously 

 long ago. 



I am particularly desirous of obtaining a good many 

 specimens of the different species of Lepidosteus, to ascer- 

 tain the range of their variations. But I know so well how 

 difficult it is for a physician to find time for anything 

 besides his business, that I beg you will consider my 

 request as made with the full consciousness that it may be 



