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CATALOGUE OF THE NAIADES OF MISSOURI. 



Family I. Margaritanidae Ortmann. 



191 1 — Margaritanidae Ortmann., Nautilus, Feb. 



"Diaphragm incomplete, formed only by the outer gills; 

 outer laminae of outer gills only in part connected with the mantle, 

 posteriorly free for considerable distance. Anterior end of inner 

 gills separated from the palpi by a wide gap. The margins of the 

 mantle do not unite or approach each other anywhere and there 

 is no tendency to form branchial and anal siphons and no supra- 

 anal opening is present. Gills without water-tubes, inter-lamellar 

 connections forming oblique rows. Marsupium formed by all 

 four gills. Glochidia small, semicircular and globular, without 

 hooks, but with irregular, small teeth at the ventral margin." — 

 Ortmann {191 2 b, p. 22 j). 



This Family presents the most primitive characters of the 

 Naiades and is represented in Missouri by only one species, Cum- 

 berlandia monodonta (Say), for which it was necessary to create 

 a special genus because of its peculiar gill structure as determined 

 by histological studies. Even in this Family, shell characters 

 are not constant enough to be considered in the diagnosis. Like 

 the sub-families, Unioninae and Anodontinae of Unionidae, the 

 glochidal discharge is effected through the anal opening. 



Genus Cumberlandia Ortmann. 



18912a — Cumberlandia Ortmann, Nautilus, XXVI pp 13 and 14. 



(Type, Unto monodonta Say.) 



Animal Characters: — Diaphragm and supra-anal opening 

 absent; gills long and narrow, inner broader anteriorily than 



