5^? 



58 DESCRIPTION OF NEW 



dining downwards, single in the right and double in the left valve 

 enlarged and truncate at the anterior end; lateral teeth rather large 

 thickened and curved in the inferior portion; anterior cicatrices 

 distinct; posterior cicatrices confluent; dorsal cicatrices placed in the 

 inferior part of the cardinal teeth ; cavity of the shell deep ; cavity of 

 the beaks angular ; nacre purple. 



Remarks. — The genus Unio has particularly attracted the attention 

 of naturalists, in the fact of its presenting specimens which resemble 

 many of the genera and species of other families. Thus we have them 

 to resemble an Area, a Venus, a Solen, a Modiolus, &c. The shell de- 

 scribed above resembles that which 1 never expected to see in the 

 Naiades, viz. the Cytherea Dione! The Unio spinosus is certainly the 

 most extraordinary species of this genus which has come under my 

 notice. Having seen but a single specimen, T am not prepared to say 

 that the number of spines is uniform. There are apparently four pairs. 

 I say apparently, for I find no antagonist spine on the right valve 

 opposed to that nearest the tip of the beak. The beak being slightly 

 eroded there, may account for its absence. That which remains on 

 the left valve, nearly a quarter of an inch from the tip of the beak, is 

 only one-tenth of an inch long, but, being fractured, may have been 

 originally much larger. This I call the first pair. 



The second pair is placed nearly half an inch from the same point, 

 and the spines directly opposite to each other. That on the left valve 

 is half an inch long, but, being fractured at the apex, most likely was, 

 in a perfect state, one-tenth of an inch longer. At the base it is nearly 

 one-tenth of an inch thick, at the top one-twentieth. That of the right 

 valve is about four-tenths of an inch long, and bifurcates two-thirds of 

 the way up, at an angle of nearly forty degrees, the apex of each branch 

 being fractured. 



The spines of the third pair are pot exactly opposed to each other 

 but this I attribute to accidental causes in this specimen. In the 

 left valve the spine is placed nearer to the umbonial slope than those 

 which are next to it, while that of the right valve is further removed 

 from it ; consequently neither stand exactly in the line of the row of 

 the whole on each valve. That of the left valve is broken off three- 

 tenths of an inch from its base ; that of the right valve is six-tenths of 



