■)0 



THE NAIADES OF MISSOURI I 87 



sisting of thirty large ovisacs distended, when gravid, at their 

 distal ends into bulging beads drawn down near to mantle flap 

 which is a long, wide, ragged ribbon that bears eye spots and 

 extends to bend of the post-ventral curve of the shell; congluti- 

 nates white, discharged in unbroken masses; glochidia medium 

 in size, semi-elliptic, with rather straight hinge line,- measuring 

 0.205 X 0.255mm. 



SHELL CHARACTERS. 



External Structures: — Shell of female sub-rhomboidal 

 greatly inflated, swollen post-ventrad, male sub-elliptic not so 

 inflated; narrowly rounded before, disk smooth, without sculpture; 

 beaks very full, very much inflated, sculptured by four coarse 

 sub-parallel bars with rounded furrows between; epidermis thin, 

 smooth, polished, yellowish, bluish olivaceous or even terra- 

 cotta, with broad brilliant green, or blue-green rays all over shell; 

 post-umbonal ridge prominent but not angled. 



Internal Structures: — Cardinals prominent, serrate, rather 

 curved; laterals erect blade-like; beak cavities very deep and 

 basin-like; nacre pure marble white, sometimes inclined to pink. 



Sex Length Height Diameter Locality 



9 100 X 65 X 45 mm — (Gasconade R., Gascondy) 



cf 90 X 65 X 42mni — (Black R., Williamsville) 



cf iio X 39 X 26mm — (Osage R., Osceola) 



9 55 X 39 X 26mm — (Miss., R., La Grange) 



The *young shells are very bright colored. The specimen 

 of the last measurement has a blue epidermis with bright blue- 

 green stripes. Its beak sculpture is very plain and eroded in curved 

 beaks showing as above described. No juveniles obtained. 



Miscellaneous Remarks: — Young shells look much like 

 vmltiradiata but can be distinguished from the latter by the presence 

 of post-umbonal ridge and by not possessing so many finer rays. 

 The adult shell is told from that of ovata by not possessing the 

 sharp cornered post-ridge, larger shell and more peculiar rays. 

 Aside from these two related shells ventricosa is unique. Muliira- 

 diata and ovata are not found in Missouri. Ventricosa is also very 

 peculiar in the structure of its soft parts — especially in the great 

 development of the mantle flap that characterizes the genus 

 Lampsilis. The writer has observed these flaps extended and in 

 action both in the aquarium and in nature. Three have been seen 



