141 2 ANODONTITES 



ANODONTrj'KS MJJMRRANACEUS (MatOll). 



Shell smal!, subinflated. thin and fragile, irregularly obo- 

 vate, almost equilateral : hinge line straight or curved down- 

 ward a little medially ; anterior end narrowed, rounded ; base 

 well rounded, fuller behind the middle ; posterior end wide, 

 rounded, joining the dorsal edge at an angle where it is pro- 

 duced into a small wing ; beaks full, rounded ; epidermis green- 

 ish, lighter colored at the umbonal region; nacre smooth, sub- 

 margaritaceous. transversely, delicately striated. 



Length 24, height 17 mm. 



Rio de la Plata. 

 Mytiius membranacciis Maton, Tr. Linn. Soc. Lond., 181 1, 



p. 329, pi. XXIV, figs. II, 12. 

 Margarita (Anodonta) incmhranacca Lea, Syn., 1836, p. 22; 



1838, p. 23. 

 Margaron (Anodonta) mcmbranacea Lea, Syn., 1852, p. 34; 



1870, p. 55. 

 Unio mcmbranacens Hani.ey, Test. Moll., 1842, p. 202. 

 Glaharis nienibranaceus Simpson, Syn., 1900, p. 919. 

 Unio subtrapc^iiis Piiilippi, Zeits. fur Mai, IV, 1847, P- 9^; 



Abbild., in, T848, p. 80, pi. V, fig. 3.— KusTER, Conch. Cab. 



Unio, 1862, p. 283, pi. xcv, fig. 4. 



Maton states that his shell is fragile and membranaceous, 

 that the nacre is transversely striate. I am not certain whether 

 he means by the last statement that it is concentrically striate, 

 showing the growth lines or that it is radially striate as is the 

 case with many species of Anodontites. It is possible that his 

 shell is but the young of some other well-known form, but I 

 know of no species of this group in which the young is fragile 

 and membranaceous. 



Anodontites i.kotaudi (Guppy). 



Shell somewhat rhomboid obovate, convex, scarcely sub- 

 solid, inequilateral ; beaks moderately full and elevated : dorsal 

 and basal outlines curved ; anterior end a little narrowed, 

 rounded ; dorsal slope obliquely subtruncate, below which the 

 posterior end is rounded ; surface irregularly, concentrically 



