kAIADES OF MISSOURI 6t 



dorsad, color of soft parts tan, for most part, mantle edges at 

 siphonal openings black, gills and parts above darker tan tha 

 parts below. 



Reproductive Structures :— Only sterile marsupia observed; 

 all four gills, however, marsupial and same in structure as that 

 of Q. verrucosa; glochidium not found. 



SHELL characters. 



External Structures :— Shell roughly pentagonal in gen- 

 eral outline, heavy, thick, solid, compressed posteriorly, inflated 

 for one-half of the shell anteriorly, obtusely biangulated behind 

 with truncation obliquely antero-ventrad, broad, shallow, radial 

 furrow , post-umbonal ridge flattened and sculptured with few 

 tubercles, area in front of radial furrow irregularly and coarsely 

 tuberculated , slopes of post-dorsal ridge with low upcurved 

 costae, epidermis dark brown, growth lines coarse. 



Internal Structures: — ^Cardinals and laterals both dis- 

 tinctly doubled in the two valves, interdentum short, wide, 

 cut away in right valve for the post-left cardinal, anterior adductor 

 muscle scars usually drawn to the front, nacre milky white. 



Sex Length Height Diameter Locality 



9 1 20 X 88 X 57mm (Marais des Cygnes R., Rich HiU,) 



cf 80 X 56 X 30 " (Osage R., Greenwell Ford) 



9 56 X 46 X 27.5mm ( " " " " ) 



No juveniles were obtained. The last measurement, is that 

 of the smallest in the writer's collection, but shows no real juvenile 

 characrters, and is more like Q. aspera except for its difference 

 in posterior biangulation and also in its tuberculation. 



Miscellaneous Remarks: — Simpson (1900b, p. 776) puts 

 Q. nobilis down in the synonomy of aspera, but later refers it to 

 0. verrucosa. However, from studies of its peculiar anatomy and 

 internal shell structures it may come very near to verrucosa. This 

 is a rather common species for the Osage where it reaches a larger, 

 heavier growth of shell than is ever attained by verrucosa. It is 

 also a broader, shorter shell with great solidity and inflation 

 anteriorly and also greater compression posteriorly. Nobilis is 

 reported by Isely (19 14, p. 4) for the lower Neosho basin. It 

 likewise appears occasionally in this same drainiage for Missouri 

 and is also found in the Grand River of North Missouri. Like R. 

 tuberculata (Raf.), nobilis may be said to have no true supra-anal 

 opening due to its lack of mantle connection between the anal and 



