S4 NAIADES OF MISSOURI 



Internal vStrucTurEs: — Cardinals more or less double in 

 both valves; laterals inclined to double also; umbonal cavities 

 deep and rounded out; nacre white irridescent. 



Sex Length Height Diameter Um. ra. Locality 



(Lake Contrary, St. Joseph, Mo.) 

 (Platte R., Agency Ford) 

 (Flat Creek, Sedalia, Mo.) 

 (Auxvasse R., Fulton, Mo.) 

 (Grand R., Utica) 



The above measurement is the smallest ever taken by the 

 author. It was discovered stranded on a sandbar, where it was 

 traced by its tiny furrowed track in the fine wet sand. Although 

 it had been but few days since its escape from its parasitic life 

 on the fish, yet it had no byssi. It would seem from this, and many 

 other instances, that neither the Unioninae nor Anodontinae develop 

 byssal threads. Three other juveniles found on this same bar 

 (measuring 11, 13 and 22 millimeters) were also devoid of byssi. 

 It has been the author's experience to find juveniles in companies. 

 The juvenile quadrnla has the general appearance of a young 

 fragosa, having a straw-colored epidermis, very pointed posterior 

 end, deeply sulcated post-ventral position, full rather double- 

 apiculated beaks, with corrugated sculpturing and placed almost 

 in the middle of the dorsal line; tubercles rather folded on anterior 

 umbonal slopes ridged on post-umbonal slopes and finely ribbed 

 on post-dorsal slopes. 



Miscellaneous Remarks: — Q. quadnda is represented by 

 many forms in this state — especially in Central Missouri; how- 

 ever, the large, heavy form that ranges from Ohio to Nebraska is 

 rather constant in the drainage basins north of the Missouri 

 River. l£ is strange that there should be such a depauperization 

 of any of these forms in South Mo. This species is found in Arkan- 

 sas but rather in the aspera form, a small quadrula such as mostly 

 seen in the Osage system. Mr. Walker thinks that the key for 

 tracing out the relative ranges of forms might be found in some 

 ancient drainage system, and varieties, such as found in Missouri, 

 ought to help solve the question. The inflated, solid and compara- 

 tively smooth variety of Q. quarula of A^orth Missouri may be 

 referred to Pratt's Udio lunulatus (Proc. Dav. Ac. Nat. Sci., I. 

 1876, p. 167, PI. XXXI, fig. i). However, this may simply be 

 the lacustrine form of the type since the fluviatile forms of North 



