18 kafinesque's 



and axis of the Unios and other bivalve shells, having been misund^- 

 stood by some, it may be needful to state that my formula is a kind 

 of abbreviation of a longer exposition. Thus when I say, length one 

 half, diameter one third, axis one fourth of the breadth — I meant 

 to say, and I must be understood to state the fallowing longer 

 account : — 



Ihe length of the shell is one half the diameter is one third, 

 and the axis is at one fourth of the whole breadth, or largest 

 dimensions of the shell. 



In longitudinal shells this is reversed, the length being the longest 

 dimension, becomes the size of comparison. 



I onght to have added to the names of our late writers on JJnio, 

 Mr. Hildreth, who has described over again a few of my species, and 

 Prof. Eaton, who I regret to say, has, (in his Zoological, Text- 

 Book, Albany, 1826, now before me,) noticed 33 species of JJnio and 

 Alasmodon of Say and Barnes, but none of my previous ones ! and 

 put them all back to the old genus Mya of Linneus ! This, as well 

 as his whole Zoological book, proves that he is forty years back- 

 wards in the science of Zoology, as he is 30 years backwards in 

 Botany, and about 20 in Geology. But this is not peculiar to him, 

 it is the fate of one half of our Naturalists, Botanists and Geologists. 

 The daily increase of knowledge and improvement in science is 

 despised or neglected by them as useless innovations ! While all the 

 world, and all the sciences move forward, they would keep those 

 they teach or cultivate at a stand ! it is all in vain, and time will 

 show it. 



II. Genus or tribe Alasmodon, 

 This fine tribe of shells of which I knew only 2 species in 1819, 

 was found rather prolific in species in 1820 and 1821. I ascertained 

 then that it was also to be divided into several genera (subgenera 

 or sections) offering many different peculiarities in the hinge. I 

 have therefore established the following 4 genera with it. 



1. Lasmigona. Cardinal tooth knobby, crenate and decurreut 

 before. Lamellar tooth remplaced by an horizontal angular pro- 

 jection, flat above. 



2. Amblasmodon. Cardinal tooth knobby, crenate and decurrent 

 before. X/amellar tooth remplaced by an obtuse oblique knob, a 

 furrow between it and the ligament. 



