THE NAIADES OF MISSOURI 



107 



but glochidia are held together in loose masses by brownish mucus 

 and coiled larval threads. 



Fig. 7. 



(X87.) 



Mature closed glochidium of L. suborhicidata. 

 SHEI^L CHARACTERS. 



External Structures: — Shell subround, or suborbicular, 

 thin, compressed, rounded before, bowed ventrad, pointed behind, 

 sulcated post-dorsad, alated, dorsal line from apex of wing to an- 

 terior end, straight and at an angle of 45 degrees; disk smooth; 

 beaks flattened, sculptured with coarse wavy bars, intermediate 

 ones bow-shaped and arched toward apex, latter double-apiculated 

 'with smaller tubercles just ventrad, later bars subundulate on 

 upper disk and running more or less parallel with growth Unes; 

 epidermis polished, straw colored in young, light brown-horn in 

 old; rayed all over with green capillary lines and one or two 

 broad bluish-green bands from beak to extreme posterior point 

 of shell; growth lines raised and undulated showing through on 

 nacreous surface. 



Internal Structures: — Cardinals and laterals entirely 

 lacking; anterior adductor muscle scars two comparatively deep 

 elongated triangular areas, progressive impressions most distinct; 

 other cicatrices very faint, confluent, mantle line broken by 

 minute ridges; umbonal cavity shallow; nacre whitish, bluish 

 or coppery, irridescent. 



Sex Length With Diameter Um. ra. 

 ? 185 X 130 X 67mm 0.290 

 cf 150 X 117 X 49 " 0.270 

 9 47 X 35 X 14 " 0.260 

 cf 34 X 23 X 9 " 0.250 



Locality 

 (Lower L. Contrary, St. Joseph) 

 (Upper L. Contrary, " " ) 



(Sugar Lake, Armour, Mo.) 

 (L. Contrary, St. Joseph, Mo.) 



The latter measurement is that of the smallest juvenile of 

 this species out of a collection of a little over a hundred of these 

 delicate shells. This one was without byssi and doubt is expressed 



