THE NAUTILUS. 17 



accessible, ample opportunity was given to obtain the most 

 complete record and has been found gravid with ripe glochidia 

 every month of the year except for March and August. How- 

 ever, high water prevented the keeping of a complete record for 

 any species during March. In all probability fragilis bears 

 glochidia throughout this month also as more individuals of this 

 species were found in glochidial gravidity during the month 

 immediately preceding than at any other time of the year. 

 Hence, we would conclude that this species is bradytictic (i. e., 

 a long-period breeder) with an overlapping breeding season. 

 Lastena ohiensis and Strophitus edentidus may be classed likewise 

 because of the same character in that they also overlap in their 

 breeding season. The fact of non-parasitism as the normal 

 habit of these last mentioned may account for their eccentricities 

 of breeding season. We may also account for the very peculiar 

 marsupial structures of S. edentidus because of this independent 

 metamorphosis of its larva. As far as now known all species of 

 Naiades, except the last named, are dependent upon fish-hosts 

 as their natural distributors ; however, the wide distribution 

 of both S. edentidus and L. ohiensis has been considered to be 

 due to the buoyancy of the placentulae, (gelatinous cords holding 

 glochidia), discharged by the former and also to the very light 

 papery shells of both juvenile and adult of the latter. 



Probably this account will show the smallest gravid individual 

 on record. On March 3, 1913, a gravid Proptera laevissima } 

 bearing mature glochidia, was collected by the writer in Lake 

 Contrary, St. Joseph, Mo., measuring 89 mm,, in length, and on 

 September 10, 1914, 61 laevissima were collected, 32 of which 

 were found gravid with ripe glochidia. Strange to say, these 

 female shells were all smaller than the other 29 males ; however, 

 none in this collection exceeded 43 mm. in length, two being 

 only 39 mm. long. Upon further study it may be found that 

 these so-called laevissima are really distinct species and that the 

 occurrence of smaller shells may be found to be normal, as seen 

 in case of Obliquaria reftexa and of Plagiola lineolata (Raf. ) 

 (=P. securis [Lea]). 



The Breeding Record kept herein corresponds with those of 



