on NAIADES OF MISSOURI 



inner laminae of inner gills free from visceral mass; palpi long and 

 broad; soft parts a light tan. 



Reproductive Structures: — Marsupia identical with those 

 of Q. quadrula. No gravid forms found. 



SHELL CHARACTERS. 



External Structures: — Shell small, subquadrate, biangu- 

 lated behind, the biangulation pointed ventrad; post-dorsal ridge 

 costated; post-umbonal ridge prominent, profusely tubercled; 

 radial furrow rather wide and shallow, bounded in front by a rather 

 scattered row of sharp tubercles; epidermis blackish. 



Internal Structures: — Identical with those of Q. nobilis 

 which are somewhat peculiar. 



Sex Length Height Diameter Locality 



9 52 X 46 X 29mm (Osage R., Warsaw, Mo.) 



cf' 44 X 39 X 27 " ( " " " " ) 



9 40 X 38 X 24 " ( " " " " ) 



Miscellaneous Remarks. — Although this species has only 

 been found in the Osage basin for this State, yet it is not to say, 

 a very common shell there. So closely related is this small form 

 of quadrula to Q. nobilis that a good series of shells may reveal it 

 as the young of nobilis. Aspera has been considered the southern 

 form of Q. quadrula and it may be the small multi-tuberculated 

 representative of the South-west which is connected geographically 

 by all forms of intergrades to that large, heavy, smoother repre- 

 sentative of the North Mississippi Valley. 



Quadrula nobilis (Conrad). 



("Big Buck Horn," "Maple Leaf.") 



PL XIX. Figs. 51 A and B. 



1854 — Unio nobilis Conrad. Jl. Acad. Nat. Sci. Phila., II, p. 297, 

 PI. XXVII, figs. 2 and 3. 



ANIMAL CHARACTERS. 



Nutritive Structures: — Branchial opening large with 

 feathered papillae, anal crenulated, supra-anal without mantle- 

 connection to anal — hence both openings virtually one, gills 

 long, rather narrow, inner laminae of inner free only one-half 

 way, palpi enormous connected two-thirds of their length antero- 



