462 THE AMERICAN M 
Sub=Family II] 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 Lampsilis Type; 
bradyitictic. 
Proptera Type 
(Intermediate to 
modern form) of 
glochidium: Axe- 
head shape, spin- 
ed-spineless. 
ee 
cr 
IDLAND NATURALIST 
Sub-Family If ANODONTINAE:— 
Marsupium differentiated with lat- 
eral water tubes when gravid; post- 
ventral mantle margin undifferenti- 
ated; all four gills marsupial; gloch- 
idium Anodonta Type; bradytictic. 
Anodonta Type 
(Intermediate 
Form) of glochid- 
ium: Subtriangu- 
lar, spined, fol- 
lowed in adult by 
incomplete hinge 
ae Based O Se 
The Spineless 32 As he 3 £2 Sub = Family | 
Bier iidia are Polen y Nee Luly eOer Oe ee eae UNIONINAE : — 
; Characters 
lowed intheadult 
life by perfect 
and compbiete 
hinge teeth. 
Lam psilis type, (Modern- 
Form) of glochidftum —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. 
Undifferentiated 
marsupium and 
post-ventral 
mantle margin; 
all four (or outer) 
gills marsupial; 
tachytictic spe- 
cies; glochidia 
Lampsilis Type. 
Family | MARGARITANIDAE:— 
Marsupium more primitive than 
that of Family II; post-ventral 
mantle margin undifferentiated; all 
four gills marsupial; glochidium 
Lampsilis Type; tachytictic 
i 
- 
2 
me) 
° 
= 
—Primitive 
