,t^ 



,7^V 



78 NAIADKS OP MISSOURI 



1912b — Pleurobema pyramidatum (Lea) Ortmann, An. Car. Mus., 

 VIII, p. 264. 



ANIMAL CHARACTERS. 



Nutritive; Structures.: — Branchial opening densely papil- 

 lose; anal finely papillose; anal and supra-anal very closely 

 connected by mantle edges — sometimes connection deciduous; — 

 inner gills broader, longer, inner laminae free from visceral mass; 

 palpi long and thickened; most of soft parts dirty white, mantle 

 edges at branchial openings black. 



Reproductive vStructures: — Only outer gills marsupial; 

 sterile marsupia with crowded septa, those of male gills very 

 distinct and more separated; no gravid specimens found. 



shell characters. 



External Structures: — Shell obliquely pyramidal or trap- 

 ezoidal, very solid and heavy anteriorly; disk smooth; beaks 

 very full and projecting anteriorly; rather straight dorsad, greatly 

 curved ventrad, epidermis black. 



Internal Structures: — Cardinals single in right, double in 

 left valve; laterals double in left, single in right; scars deeply 

 impressed; beak cavities moderately deep; nacre white, tinged with 

 blue posteriorly — sometimes pinkish. 



Sex Length Height Diameter Locality 



cf 6,5 X 55 X 40mm (Osage R., Sagrada) 



'9 73-5 X 52.5 X 42 " ( " " Warsaw) 



9 63.5 X 54 X 39 " (Meramec R., Fern Glen) 



cf 27.5 X 26.5 X i9.5mni (Osage R., Baker) 



Juvenile shell thick, almost globular, very smooth; beaks 

 full but not protruding anteriorly, sculptured with two or three 

 ridges arranged rather concentrically and breaking into three 

 coarse tubercles at base of post-umbonal ridge; epidermis reddish 

 and leather-like with rays on the anterior half of shell; lateral 

 teeth more inclined to double in right valve than in mature shell; 

 beak cavities very shallow; nacre solid pink. 



Miscellaneous Remarks: — This pyramidatum is the same 

 as found in Arkansas and Oklahoma where it is also found unasso- 

 ciated with typical obliquum. The species, Pleu. pyramidatum 

 (Lea) and obliquum (Lam.) are most typically represented in the 

 Tennessee-Cumberland system and the fact of their forms turning 

 up in the South West (i. e., in the region south of the Missouri and 



