■.jC 1 80 THE NAIADES OF MISSOURI 



Reproductive Structures: — Marsupium rather reniform 

 occupying over posterior half of outer gills and consisting of sixty- 

 five ovisacs well separated, when gravid extending below original 

 ventral edge of sterile marsupia ; inner mantle edge antero-ventrad 

 to branchial opening a specialized flap reaching down to lowest 

 point of the post-ventral part of shell where it is developed into a 

 tentacular lobe; conglutinates white, sole-shaped, not very solid, 

 glochidia medium in size, sub-elliptical, spineless, hinge line rather 

 short, evenly curved, measuring 0.185 ^ 0.210 mm. 



SHELL CHARACTERS. 



External Structures: — Shell elongate-elliptic, medium in 

 size, subsolid, disk smooth; umbones large, but not full, sculpture 

 by five or six double looped or sickle-shaped ridges most pronounced 

 and opened at base of post-umbonal slope; epidermis straw-color 

 (usually without much display of rays) smooth, polished; female 

 shell much produced at the post-ventral edge of shell and continued 

 upward as a marsupiual inflation for a short distance; male shell 

 pointed posteriorly. 



Internal Structures: — Cardinals prominent, serrate, double 

 in right valve, single in left; beak and branchial cavities rather 

 deep and basin-like; nacre satin-white, irridescent posteriorly. 



Sex Length Height Diameter Locality 



cT^ 120 X 60 X 45mm — (Chariton R., Kern) 

 9 100 X 50 X 38mm — (Miss. R., Hannibal) 

 50 X 23 X i6mm — (Grand R., Darlington) 

 12.5 X 6 X 5nim — (Grand R., Utica) 



The last measurement was that of one of the smallest juveniles 

 obtained by the writer. It has a black border to its shell and a 

 short byssus extending from between the valves at ventral portion 

 of shell. 



Mi'CELLANEous REMARKS: — Even in the juvenile anodon- 

 toides there is some difference from that of the fallaciosa shell 

 in that there are not as evident. The main distinction between 

 the adult shells of these two species is that 'of jallaciosa is bril- 

 liantly rayed, is smaller, has more reddish beaks and is a dweller 

 in muddy creeks, sloughs and lakes while anodontoides loves sandy 

 situations of swifter water and develops a large, thick shell, rayless, 

 unicolored epidermis and is a most active mussel. When perfect 

 (as it is found in the Chariton and Mississippi Rivers) it is one of 



