THE NAIADES OF MISSOURI 16^ 



sisting of twenty ovisacs, well marked, occupying posterior half 

 of outer gills, somewhat distended transversely and also at distal 

 ends below the original line of sterile marsupium ; border of mantle 

 antero-ventrad to branchial opening greatly specialized into a 

 double row of red papillae terminating in a knobbed caruncle, 

 which, under (xSy) lens, is cellular — each cell being hexagonal in 

 shape; conglutinates white, discharged whole, club-shaped, 

 glochidia medmm in size, sub-elliptical, hinge line straight, spineless, 

 measures o.iyj x o.ioo. 



SHELL CHARACTERS. 



External Structures: — Shell very small, rather thick, 

 elliptical, rounded before, disk without sculpture; beaks low with 

 six coarse regular, parallel bars evenly curved up at foot of post- 

 ridge region; epidermis brownish to reddish or olivaceous, cloth- 

 like female shells broader posterior ends made by more swollen 

 post ventral portion, males with pointed shells. 



Sex Length Height Diameter Locality 



* 38 X 23 X 19mm (Lake Contrary, St. Joseph — ) 

 cf 27 X 13 X iimm (Pond, Columbia) 



* 25 X 13.5 X 11.5mm (Lower L. Contrary, St. Joseph) 



* 14.5 X 8.5 X 5.5mm (Singleton Lake, Halls) 



* 1 1.5 X 6.5 X 4.0mm ( " " " ) 



The writer obtained about forty juveniles, within the range 

 of the last two measurements, in shallow clear water along the 

 northwest shore of Singleton Lake. They were confined to a small 

 space and were traced here and there among a maze of tiny tracks. 

 These juvenile shells differ from the adult by a thinner shell, more 

 pointed posteriorly, a more greenish epidermis, more compressed, 

 and by a coarser beak sculpture which, although arranged the same 

 in its concentric bars curved up posteriorly, yet they extend down 

 well on the center of the disk. (See PL III, fig. 8c). 



Miscellaneous Remarks: — The ivriter is able to bear out the 

 statements of Drs. Sterki and Ortmann that parva is locally herma- 

 phroditic. In the past three years, hundreds have been collected 

 in nearly all the Northwest Missouri lakes and streams, but not 

 a single one has been found without the marsupial character of 

 gills and the sexually dimorphic female shell. However, the male 

 and female shells appear in Central Missouri. In all specimens 



* This symbol (*) would indicate hermaphroditism here. 



'1 



