^ 



Sub=Family III LAMPSILINAE:— 



Marsupium differentiated with 

 special ovisacs mostly arranged post- 

 eriorily near the post-ventral mantle 

 margin specialized with crenulations, 

 papillae, etc. ; only outer gills marsu- 

 pial; glochidium Lamp'u'lis Type; 

 hrddvtictic. 



Proptera Type 

 (Intermediate to 

 modern form) of 

 glochidium: Axe- 

 head shape, spin- 

 ed-spineless. 



Sub=Family II ANODONTINAE:— 



MarsujMum differentiated with lat- 

 eral water tubes when gravid; j^ost- 

 ventral mantle margin undifferenti- 

 ated; alMour gills marsupial; gloch- 

 idium A)wdon!a Type: hradytictic. 



The Spineless 

 glochidia are fol- 

 lowed in the adult 

 life by perfect 

 and complete 

 hinge teeth. 



Lamps His type, (Modern 

 Form) of glochidium :-Suboval- 

 subelliptic, spineless. 



This reversion of the modern form 

 of glochidium to that of the primi- 

 tive very strikingly shows that ata- 

 vism characteristic of the principles 

 of evolution. 



Anodonta Type 

 (Intermediate 

 Form) of glochid- 

 ium: Subtriangu- 

 lar. spined, fol- 

 lowed in adult by 

 incomplete hinge 

 teeth. 



—Primitive 



Sub = Family I 

 UNIONINAE: — 



I'ndifferentiated 

 marsupium and 

 post-ventral 

 mantle margin; 

 all four (or outer) 

 gills marsupial; 

 ta chyt i ct ic spe- 

 cies; glochidia 

 Lamp si lis Type. 



Family I MARQARITANIDAE: — 



Marsupium more i)rimitive than 

 that of Family II; post-ventral 

 mantle margin undifferentiated; all 

 four gills marsupial; glochidium 

 Lampsilis Type; tachytictic 



