THK NAUTILUS. 



119 



2. Genera: Ohliquaria (Raf.) Simps — Plagiola (Raf.) Ag.— 



Obovaria (Raf.)^ 

 Species : Ohliquaria rejlexa Raf. 



Plagiola securis (Lea) — elegans (Lea). 



Obovaria retusa (Lam.) — circulus (Lea) — ellipsis 



(Lea). 

 Obovaria ligamentina (Lam.)' 



3. Genus : Proptera Raf. ' 



Species : gracilis (Barn.) — alala (Say. 



4. Genus: Caz-Mwctf/iwa Simps, (subgen.) 

 Species: parva (Barn.)* 



5. Genus : Micromya (Ag.) Simps. 

 Species : fabalis (Lea.) * 



6. Genus . Lampsilis Raf. (restr.)* 



Species : iris (Lea) — nasuta (San) — recta (Lam.)' 



luteola (Lam.) — radiata(Ginel) — orbiculata (Hildr.)' 



' These three genera are practically identical with regard to their anatomy, 

 only Ohliquaria is distinguished by the marsupium consisting only of a few 

 ovisacs. They may be distinguished by shell characters, which, however, are 

 hard to define. All the species enumerated here are characterized by the 

 absence of papillce or flaps on the mantle edge in front of the branchial opening. 

 A final arrangement of the genera must be left for the future. 



» Obovaria ligamentina = Lampsilis ligamentina. This species undoubtedly 

 belongs into this group, and not with the true Lampsilis. 



'^Proptera, as defined by Sterki. F. alata is distinguished by its peculiar 

 glochidia (rectangular, with two spines). But P. gracilis, which agrees in all 

 other respects, has different glochidia; they are of the normal Lampsilis-shape, 

 but much smaller. 



* Car. parva has the inner lamina of the inner gills not connected with the 

 abdominal sac, and the supra-anal opening is entirely closed ; for the rest it 

 resembles the tm-type of Lampsilis. 



^Micromya fabalis agrees well with the tVw-type of Lampsilis, but the inner 

 lamella of the inner gill is partly free from the abdominal sac. Both Caruncu- 

 Una and Micromya form a transition from the more primitive forms to the 

 typical Lampsilis. Further study possibly will throw more light upon these 

 forms. 



^Lampsilis is characterized by the development of peculiar structures on 

 the mantle edge. The first group has papillae, the second a flap. 



' Also Lampsilis vibex nigrina (Lea) from Florida and L. anodontoides (Lea) 

 from Texas have been investigated, and prove to belong to this group. 



8 L. orbiculata is not at all related to L. ligamentina, as Simpson thinks, but 

 it belongs to the ventricosa group of Lampsilis, for it has a well-developed flap 

 on the mantle edge. 



