﻿52 2 MAKC.AKIT.WA 



Uniu monodontns Say, Am. Conch., V'l, 1834. — Hani,i;y, Biv. 



Shells, 1843, p. 210, pi. xxiii, hg. 48. — KusTiiu, Conch. Cab., 



18O1, p. 221, pi. lyxxv, tig. I. 

 Margarita (UnioJ monodontus L,iv\, Syn., 1836, p. 40; 1838, 



p. 20. 

 Alargarun (UnioJ monodontus iyiiA, Syn., 1852, p. 39; 1870, 



p. 62. 

 Unio soleniformis Lea, Tr. Am. Phil. Soc, IV, 183 1, p. 87, pi. 



X, lig. I7J Obs., I, 1834, p. 97, pi. X, fig. 17.— Chenu, 111. 



Conch., 1858, pi. xi\o figs. 4, 4a, 4.b; Manual II, 1859, p. 137, 



fig. 661. — SowERiJY, Conch. Icon., XVI, 1866, pi. xlv, fig. 



243- 

 Margaritana soleniformis P^Tivi^, Conch. Sam., 1890, p. 173. 



The anterior end of old shells is often much more solid than 

 the posterior. Longer in proportion than any other Margari- 

 tana. 



Dr. Ortmann (1. c.) has recently made this species the type 

 of a new genus, Cnmberlandia, which he separates from Mar- 

 garitana on account of the greater development of the gill 

 structure. He says : "While in other species of the genus 

 Margaritana the interlaminar connections of the gills are scat- 

 tered, and irregularly distributed, or fall into more or less dis- 

 tinct oblique rows, in the present species these irregular, inter- 

 rupted rows are developed as continuous septa, tvhich rim 

 obliquely forzcards. In the middle of the gills these septa are 

 well developed and quite continuous, but rather distinct from 

 each other. Towards the ends of the gills they are more irreg- 

 ular, shorter and chiefly at the posterior end they are somewhat 

 interrupted, and thus it is clearly seen that they represent a 

 further development of the oblique, interrupted rows present 

 in other species of Margaritana." 



Group of Margaritana decumbens. 



Shell trapezoidal, thin, compressed, pointed at the posterior 

 base ; hinge line sinuated. 



Margaritana decumbens (Lea). 



Shell irregularly rhomboid or trapezoid, being narrowed in 

 front and somewhat widened behind, compressed, scarcely 

 subsolid, inequilateral, somewhat arcuate; beaks neither full 



