' o 



118 The naiades of MISSOURI 



outer, the whole pad-like; gills large, inner semi-circular, free 

 from the abdominal sac or united with it; branchial opening 

 large with many small, papillae; anal with well developed papil- 

 lae.'^ (Simpson. 



SHELL CHARACTERS. 



External Structures: — Shell sub-elliptical inflated, thin; 

 disk smooth; beaks somewhat full with distinct beak sculpture 

 consisting of concentric ridges upcurved behind; epidermis dark 

 brown, polished, sometimes rayed; hinge-teeth lacking, or merest 

 rudiments, scars shallow; nacre bluish white. 



Dr. Ortmann considers this genus pratically an Anodon with 

 concentric beak sculpture and as a good connecting link for Ano- 

 donia and Alasmidonta. The only species of this genus, Jerussaci- 

 anus, is only represented along the Mississippi of this state where 

 it is a rare shell. Unfortunately the soft parts, have not been 

 secured for description. The glochidia of the species and sub- 

 species (subcylindricus) of this genus have the same shape and 

 measure 0.32 and 0.33mm. respectively — height and length being 

 equal. 



Anodontoides ferussacianus (Lea). 

 ("Ferussac's vShell.") 

 PL III, Figs, ya—Sa. 



1834 — Anodonta ferussaciana Lea, Tr. Am. PhiL Soc. V, p. 45, pL 



VI, fig. 15. 

 1898 — Anodontoides ferussacianus (Lea) Baker, MolL Chicago, 



Pt. I, p. 72, pL III, fig. 6; V, fig. 2. 



ANIMAL CHARACTERS. 



According to Dr. Ortmann (1912b, p. 294) the anatomy of 

 this species is essentially that of Anodonta and differs only in the 

 shorter mantle connection between the anal and supra-anal and 

 in the anal being distinctly papillose. The glochidia (Ortmann 

 i8iib, pi. 89, fig. 12) are described as rather small (0.320 x 0.320 

 mm.) for the subfamily, subtriangular and spined. 



SHELL CHARACTERS. 



External Structures: — Shell subelliptical, thin, inflated, 

 medium in size, post-umbonal ridge rather faint; compressed 

 with distinct, regular, concentric ridges bent up behind and api- 

 culated at the apices; epidermis brownish to bluish-green, some- 



