﻿MARGARITANA 52 1 



Margaritanopsis laoensis, Haas, Con. Cab., Unio, 1910, pi. xri, 



figs. I, 2. 

 Unio sula Theobald (where?) 



Smaller than niargaritifcra, with a higher and much wider 

 posterior ridge and always having laterals. The nacre is much 

 clearer than that of margariiifera. An undoubted Margari- 

 tana notwithstanding its peculiar geographical distribution. 



Haas has recently, ( Nachr. Deutsch. Mai. Ges., 191 3, p. 33), 

 made this species the type of a new genus, Margaritanopsis. 



Margaritania monodonta (Say). 



Shell greatly elongated, arcuate, sometimes subinflated, in- 

 equilateral, subsolid to solid ; beaks a little elevated but not in- 

 flated, their sculpture consisting of strong, straight ridges 

 running parallel with the growth lines ; posterior ridge full, 

 curved and ending behind at the base of the shell in front of 

 the hinder end ; anterior and posterior ends rounded ; surface 

 sculptured with rude growth lines ; epidermis greenish-brown 

 and subshining in the young shell, blackish, thick and dull in 

 old shells ; pseudocardinals imperfect, generally reduced to a 

 single imperfect spur or low tubercle in each valve of the old 

 shells ; laterals blurred and feeble ; there are usually two in the 

 left valve and one in • the right ; nacre white, granular and 

 pitted ; muscle scars impressed, the anterior ones rough, the 

 posterior elliptical. 



Length 172, height 53, diam. 38 mm. 



Ohio; Cumberland, and Tennessee river systems; Illinois; 

 eastern Iowa; Nebraska? 



Type locality, Falls of the Ohio and Wabash River. 

 Unio monodonta Say, N. Harm. Diss., II, 1829, p. 293. — Say, 



Am. Conch., I, 1830, pi. iv. — Chenu, Bib. Conch., ist. sen, 



III, 1845, P- 12, pi. II, fig. I 

 Alasmodonta monodonta Fejjussac, Guer. Mag., 1835. p. 26. 

 Margaritana monodonta Conrad, Pr. Ac. N. Sci. Phila.. VI, 



1853, p. 262. — Simpson, Syn.. 1900, p. 679. — Ortmann, 



Ann. Car. Mus., VIII, 1912, p. 233, figs. 2, 2a. 

 Cumberlandia monodonta Ortmann, Naut., XX\^I, 1912, p. 



13- 



