82 IOWA ACADEMY OF SCIENCES. 



KHchihita, and tapijaniana,^n(\ LampsiJis iiasutiis a,nd oc/ira- 

 ceus from Pennsylvania waters are included. Two of 

 these examinations, as indicated in the accompanying 

 tables, occurred in September. 



Table I. shows the distribution of the material exam- 

 ined by species, sex, and time of observation. In addition 

 to the fourteen hundred and ninety-eis-ht included, thirty- 

 one were excluded because the determination of sex was 

 impossible through infestation of the sexual organs by 

 parasitic cercaria to the utter atrophy of the germinal 

 tissue. A single individual of Q. tn'gona was hermaphro- 

 dite. 



Table II. exhibiting the findings, is largely self-explana- 

 tory. The similarity of the closely related forms, in their 

 time of maturity and method of carrying the young, ia 

 apparent. Because in certain species, the old glochidia 

 are found still in the marsupium when examined in May, 

 it is inferred that in these cases they have been carried 

 through the preceding winter. 



Furthermore, though this is not shown in the tabula- 

 tions, for the reason that in most species throughout the 

 time of sexual maturity a sufficient number of both sexes 

 are in a condition plainly unripe, and because of the 

 absence of the glochidia and swollen gills containing 

 them in certain females, when others of their species are 

 normally gravid, it is believed that the period of sexual 

 maturity does not always recur every year. 



