668 PROCEEDINGS OF THE ACADEMY OF [DeC, 



Anodontites bartschi n. sp. PI. XXVII, 3, 4. 



Shell small, uniformly thin, obliquely subelliptical, moderately 

 full, inequipartite; rather smooth, the growth lines being fine and 

 low, and with obsolete radiating lines produced by a peculiar wrinkle 

 striation irregularly placed, which is not constant, having largely 

 disappeared from the type; epidermis thin, light yellow-olive to 

 dark yellow-olive, rayless; posterior ridge low, with a small, sharp 

 duplication, posterior sulcus shallow; anterior margin subangulate 

 above, regularly and slantingly rounded into the base, the outline 

 of the base becoming nearly straight posteriorly; posterior margin 

 obliquely truncate, forming a straight line contained 2| times in the 

 greatest length; obtusely angulate above, terminating below in a 

 rather broad posterior point; upper margin and hinge line slightly 

 curved; edentulous with a very narrow, thin ligament; beaks rather 

 full, eroded, but apparently smooth; beak cavities moderate, cica- 

 trices indistinct, the anterior very large; pallial line indistinct; nacre 

 silvery-white, not brilliant, but slightly iridescent throughout. 



Animal unknown. 



Greatest length 35.5, width 25, diam. 14 mm. 



Three specimens of this species, all probably somewhat immature, 

 taken at Boim e Pinhel, on the left bank of the Rio Tapajoz, were sent 

 from the Goeldi Museum. The species differs from all the round 

 species of Anodontites by the truncation of the posterior extremity. 

 It is named for Dr. Paul Bartsch, of the National Museumi. 



Anodontites sp. undet. 



A single specimen of this genus, taken with the preceding, too young 

 to identify, but not corresponding to any of the foregoing species, 

 was sent from the Goeldi Museum. 



Appendix: Notes on Gundlachia Pfr., by H. A. Pilsbry. 



The peculiar Ancyloids known as Gundlachia have been the occa- 

 sion of some speculation and difference of opinion among concholo- 

 gists. That Gundlachia is dimorphic, sometimes maturing as an 

 Ajicylus without the intervention of a septate stage, was first 

 intimated by Guppy in 1870 ^ and later by several other naturalists. 

 It was observed by the present writer about 1886,- and recently by 

 Mr. J. A. Allen, who proved the identity of the septate and non- 

 septate forms by breeding them in jars. 



^ Guppy, American Journal of Conchology, VI, 1870, p. 311. 

 2 Pilsbry, Nautilus, IX, 1895, p. 63. Cf. also Bryant Walker, Nautilus, XXI, 

 1907, p. 14. * 



