■2J. 



THE NAIADES OF MISSOURI IO9 



Illinois, and Louisiana. Dr. W. S. Strode reports it as very large 

 typical and abundant in Illinois and the fact of its southern range 

 to Louisiana (as reported by Mr. Frierson) is interesting. Although 

 this mussel is very susceptible to the attacks of the parasite, 

 Atax, its shell is hardly ever distorted for that reason; neither 

 is the shell hardly ever eroded or injured by chemical reaction. 

 An accurate breeding record, kept by the writer, shows it to be a 

 long period breeder, but not so long or continuous as that of Las. 

 ohiensis ( = imbecillis.) It is found to be with early and late embryos 

 from September to December, and mature and immature glochidia 

 from December to March, but sterile for the remaining months. 



Lastena ohiensis Rafinesque. 

 ("Paper Pond Shell.") 



PI. XXIII, Figs. 74 A and B. 

 1820 — Lastena ohiensis Rafinesque, Ann. Gen. Sci. Brux., V, p. 316. 

 1829 — Anodonta imbecillis Say, N. Narm. Diss. II, p. 355. 



ANIMAL CHARACTERS. 



Nutritive Structures: — Branchial opening with yellowish 

 tentacles pointed upward, anal narrow, smooth supra-anal small, 

 far removed from anal; outer and inner gills about the same size, 

 inner laminae free from visceral mass; palpi long, sickle-shaped, 

 united antero-dorsad about two-thirds of its length ; foot, adductors 

 branchial opening region orange color, rest of soft parts tannish 

 or dirty white. 



Reproductive Structures: — Marsupia rusty brown and 

 pad-like with water-tubes and undivided ovisacs when gravid; 

 mantle edge antero-ventrad smooth without sexual specialization; 

 glochidium golden russet, broadly spadiform, spined, hingle line 

 straight, longer than high (0.310 x 0.290mm.); no conglutinates; 

 glochidia enmeshed in a tangle of larval threads. 



SHELL characters. 



External Structures :—vShell subelliptical and subcylin- 

 drical, thin, inflated, slightly alated; disk smooth, shinning; 

 beaks flush with dorsal line sculptured with coarse looped bars, 

 later ones being finely tuberculated, apex doubly apiculated; 

 epidermis grass green, to olive with post umbonal slope marked 

 by two or three bluish parallel rays. 



Internal Structures:— Teeth entirely lacking; muscle 



