18 



SYNOPSIS OF 



QUADRATE. 



arcseformis. Lea. 

 Unio nexus.* Say. 



TRIANGULAR. 



triangularis. Bar. Eat. Hild. Say. 

 Unio formosus.t Lea. (Male.) 

 Unio cuneatus. Swain. 



elegans.J Lea. 



donaciformis.§ Lea. 



zigzag. Lea. Eat. 



heterodon. Lea. 



* Say and Conrad both commit the error of giving precedence to nexus. 

 My description of arcseformis is in my memoir, read before the American 

 Philosophical Society, May 20, 1831, while Mr. Say's was first described in 

 the Transylvania Journal of December 1831. Subsequently he republished it 

 in his American Conchology, No. 6, where he places erroneously the date of 

 1832 to my memoir. 



•j- Mr. Barnes's description of triangularis was made from a female 

 shell, and mine from the male. There being an obvious distinction of the 

 sexes in every specimen, my error was a very natural one, as we had no idea 

 at the time of sexual dijfferences in the JVaiades. 



i Mr. Say thinks that Mr. Barnes's undulatus, Var. a., is the same with 

 elegans. I think differently, and would fortify my opinion in the fact, that 

 Mr. B. does not mention the zigzag rays which are strikingly singular in the 

 elegans, and could not have failed to have elicited his remarks had it been 

 under his eyes. 



§ I have expressed my doubts, Transactions of the American Philosophical 

 Society, Vol. IV., page 84, (page 94 in " Observations on the Genus Unio," 

 &c.) if this be more than a fine variety of zigzag, (nobis.) Mr. Say gives it 

 as a synonym to nervosus, Raf., and Mr. Conrad as truncata, Raf. 



