1388 MONOCONnVI..T'A 



Margarita (Ma'-garitana) paragiiayana Lea. Syn., 1838, p. 27. 

 Unio paragnayana Hanley, Biv. Shells, 1843, p. 212, pi. xxii, 



fig. 17. — SowEREY, Conch. Icon., XVI, 1866, pi. ui, fig. 273. 

 Margaron (Monocondylcca) paragnayana 1-,%a, Syn., 1852, p. 



45 ; I'^^/O. p. 7?,- 

 Unio Paraguayan us Catlow and Reeve, Conch. Nom., 1845, 



p. 62. 



A large, solid, subquadrate species, with brilliantly iridescent 

 nacre, of which M. ininuana is, perhaps, but the young. There 

 are often two faint, green rays on the dorsal slope of each 

 valve. 



MoNOCON'DYi,.iiA MiNUANA d'Orbiguy. 



Shell irregularly rhomboid, convex or subinflated, solid, 

 concentrically striate, inequilateral ; beaks quite prominent, 

 turned inward and forward ; posterior ridge rounded ; dorsal 

 line behind the beaks nearly straight ; anterior end narrowed 

 and rounded ; base lightly curved ; posterior end obliquely 

 truncate ; epidennis greenish ; nacre pale greenish or tinted 

 with reddish ; tooth of the left valve roughened. 



Length 46, height 28, diam. 20 mm. 



Rio de la Plata drainage. 

 Monocondylcra niiuuana d'OKBiGNY, Guer. Mag., 1835, p. 37; 



Voy. Am. Mer., 1843, p. 612, pi. exx. figs. 8-10. 

 Margarita (Margaritana) minnana Lea, Syn., 1838, p. 28. 

 Margaron (Monocondylcca) minnana IvEa, Syn., 1852, p. 45 ; 



1870, p. 72,- 

 Unio minuaniis Hanley, Biv. Shells, 1843. p. 213, pi. xxii, 



fig. 18. — SowERBY, Conch. Icon., XVI, 1868, pi. xci, fig. 497. 

 Monocondylcca paragnayana, (part), Simpson^ Syn., 1900, p. 



911. 



I formerly believed that this species was the same as para- 

 gnayana, being only the yoimg of it. It is however more 

 elongated, and. perhaps, less inflated than that. The dorsal 

 slope is more obliquely truncated. 



