NAIADES OF MISSOURI I9 



nae, in that the morphology of the Lampsiline glochidium would 

 indicate a reversion to the primitive type as is the natural course 

 in the cycle of evolution. Thus on the basis of glochidial characters, 

 the Family Unionidae may be grouped as: 



I Anodonta, bearing non-conglutinated glochidia, spadi- 

 form, spined. 



2. Proptkra, bearing conglutinated glocliidia, celtiform. 



spined or spineless. 



3. Unio-Lampsilis, bearing conglutinated glochidia, apron- 



form, spineless. 

 The key to the whole situation governing the approach to 

 the modern arrangement is in the differentiation of structures for 

 the benefit of the embryos; e. g., large palpi for the Unionifiae, 

 marsupial water tubes (secondary) and also large palpi for Anodon- 

 tinae, but, best of all, an adjustment of marsupium near to a special- 

 ized mantle edge in form of flaps, papillae, tentacles, etc., as 

 shown in Lampsilinae. 



I — ^Sub-Family Unioninae Ortmann. 



1911a — Unioninae Ortmann. An. Car. Mus., IV, pp. 335-336; 1912b 

 An. Car. Mus. VIII, pp. 236-277. 



Animal Characters: — Branchial opening rather sparingly 

 papillose; anal smooth to finely crennulate; supra-anal usually 

 present separated from anal by very short or moderately long 

 mantle connection ; no tendency to form tubular siphonal openings ; 

 inner laminae of inner gills free from visceral mass; palpi usually 

 very large and long, marsupium occupying all four gills or by the 

 two outer ones, when gravid not much swollen, ventral edge 

 pointed, never bluntly distended and secondary water-tubes 

 never developed lateral to the ovisacs within ; mantle edge antero- 

 ventrad to branchial opening, smooth; glochidia of the Lampsilis 

 type, apron-shaped, small to medium, semicircular or semielliptical, 

 ventral margin rounded, without spines; conglutinates well 

 formed. 



vShell Characters: — Forms of shell various, usually thick; 

 disk smooth to very profusely scuptured; beaks usually scuptured 

 with concentric or zigzag ridges; hinge teeth very highly developed, 

 cardinals and laterals never lacking; scars well impressed. 



Miscellaneous Remarks: — The soft anatomy of the species 

 of this subfamilv are rather constant. However, its shell characters 



