100 THE NAUTILUS. 



dreds of individuals were collected in April, May, August, Septem- 

 ber, October, but no gravid females were among them. 



Unto crassidens Lam. Summer breeder (Sterki, '95). 1 collected 

 numerous specimens in July, August, September, October, but never 

 found a gravid female. I never had a chance to get this species 

 earlier in the season. 



Unio complanaius Dillw. " But once annually, from April-May 

 to July-August" (Conner, '07); May (Lea, X, '63). I collected 

 this species only in the month of August, and consequently never 

 found it gravid. 



Pleurobema clava Lam. July-August (Lea, III, '42). Found 

 gravid on June 18 and July 10. Specimens collected on May 14 

 and in August, September and October were not gravid. 



Pleurobema aesopus Green. Summer breeder (Sterki, '95). 

 Gravid on July 3 and 13, '08. Never found in the gravid state 

 during August, September, October, when many were collected. 



Sterki ('95) places this with the species, in which all four gills 

 are charged, and (Pr. Ohio Ac, 4, '97, p. 391) with the genus 

 Quadrula. Yet according to my observations only the outer gills 

 serve as marsupium, and are distinguished at that time by a very 

 peculiar red color; already Lea (X, '63, p. 432) enumerates this spe- 

 cies among those which have red eggs, but he saw them only in the 

 ovarium. Yet this " red " of the gills is entirely different from that 

 of certain gravid species of Quadrula, being rather of a " lilac " hue. 



Quadrula undulata Barn. Summer breeder (Sterki, '95). I col- 

 lected many specimens in August, September, October, but did not 

 find gravid females. The only one was found on July 3, '08; it had 

 all four gills charged, which were whitish (not red). 



Lea (X, '63, p. 417) says that only the outer branchiae serve as 

 marsupium, while Sterki ('95) puts it in group B, where all four 

 branchiae are said to be charged. 



Curiously enough, Sterki ('95, p. 93) places the closely allied U. 

 multiplicatus Lea (= Q. heros Say) with his group A (winter 

 breeders), giving the date November 1, and says that also the mar- 

 supium is of the type A {^LampsiUs type). Since tlie latter has been 

 described and figured by Lea (VII, '60, p. 122, pi. 30, f. 105), and 

 is distinctly of the Quadrula type, with all four gills charged, I believe 

 that we have to deal with a lapsus calami for U. muUiradiatus Lea. 



Quadrula lachrymosa Lea. May (Lea, III, '42). 



