JO Ih'ii'iCrsity of Michifj'in 



PlectomErus trapezoides Lea, 1831 



Uniu crassidcns var. a. Lamarck, '19, p. 71. 



Unio dombeyana Valenciennes, '27, p. 227, pi. 53, figs, i, i", i^. 



Unto trapezoides Lea, '31, p. 69, pi. 3, f. i. 



Unio interruptus Say, '31", p. 525. 



Unio (Bariosta) ponderosus Rafinesque, '31, p. 2. 



U. trapezoides Lea =: U. interruptus Say, Conrad, '34, p. 72. 



U. crassidens var. a Lam, ^= U. trapezoides, Lea, Lea, '34. p. 87 (type 

 examined). 



U. trapezoides Lea = f/. crassidens var. a Lam. = t'. interruptus 

 Say, Ferussac, '35, P- 27. 



U. dombeyana Val. := [7. plicafa Say, Ferussac, '35, p. 27 (type lost) ; 

 = Q. her OS Say var., Vanatta, '10, p. 102. 



Plectomerus crassidens (Lam.) = [/. interruptus Say = f ^ trape- 

 zoides Lea, Conrad, '53, p. 261. 



Bariosta ponderosus Raf. =; U. crassidens Lam. = U. trapezoides Lea, 

 Frierson, '14", p. 7. 



Quadrula trapezoides Lea = U. crassidens var. a Lam. = U. dom- 

 beyana Val., Simpson, '14, p. 830. 



Quadrula trapezoides (Lea) = U. crassidens Lam., Utterback, '16, 

 p. 88, foot-note; Walker, 'i8e, p. 174. 



Our acceptance and adoption of Dr. Pilsbry's opinion as 

 to the recognition of Lamarck's Unio crassidens carries with 

 it the retention of Lea's name for this species. 



The original description of Unio ponderosus is entirely 

 inadequate for the recognition of the species as between Unio 

 crassidens Lam. and Unio trapezoides Lea. 



The proportionate dimensions given by Rafinesque for his 

 Unio nigra {crassidens Lam.) and his U. ponderosus are the 

 same, as they are in fact, in crassidens and trapesoides. The 

 difiference between the two species being that in crassidens the 

 greatest height is at the anterior third of the shell, while in 

 trapesoides it is at the posterior third. 



Rafinesque in his generic diagnosis of Bariosta states that 

 it has the form of Scalcnaria. The only identifiable species of 

 that genus is scaleniiis, of which he gives a figure. While 

 there is not much reliance to be placed on his figures for exact- 



