ORTMANN : SUUTH AMERICAN NAIADES. 455 



originated on the old connecting land between Asia and Australia (Sino-Australian 

 continent) or in Australia, and that Diplodon first reached Chile (in Mesozoic times) 

 coming from Australia, and subsequentlj^ invaded the Brazilian mass. The 

 modern forms of the Hijriimc {('(t.slalia, Ilyria) chiefly have their center in the 

 basin of the Amazon, a comparatively young part of the continent. 



The more advanced type, represented by the subfamily Mutelince, developed 

 probably in Brazil at the end of the Mesozoic, when it liad a chance to spread 

 over the old connection across the Atlantic (Archhelenis of Von Ihering), and the 

 immigration of this stock into Central America is of rather late date (late Tertiary). 

 It is not v(M-y likely that the Mutelince reached South America coming from Africa, 

 because there is no trace of them found in southern Asia.* 



Diagnostic Characters of the South American Naiades. 

 (See Text-figiu-es 1, 2, 3.) 

 Family: MUTELID^ Ortmann (1911). ^ ' 



1. Diaphragm between branchial and cloacal cavity formed anteriorly by the 

 gills, posteriorly by a solid union of the mantle margins (Figs. 1, 2, 3, t). (No such 

 mantle connection in Unionidiv). 



2. Anterior end of inner gill (Figs. 1, 2, 

 3, i) broadly attached, and in contact with 

 posterior base of palpi (h). (In the Union- 

 idce, there is always a longer or shorter space 

 between these parts.) "" ^ t 



3. Anal and branchial openings (a and Vm. i. Diagram of soft parts of fciiiale 

 b) sharply separated from each other by the of Diphdon irijidi's (l^ca). Natural si/.c, 



p ,1 ,1 • /.< r<i „ .„4„„ left section of mantle removed, a, Anal 



union of the mantle margms (See Character . , „ , . . 



opening; b, Branchial opening; ft, Palpi; i, 



1); anal opening open or closed above, but j,^,^^^. ^j,,. ^^ ^^^^^ ^^^. ^^ p^^. ^_ Closed 



there never is a supra-anal opening. (In the part of anal opening; t, Union of mantle 

 JJnionidoe, the anal may be open, but, when separating anal and branchial openings. 



closed, there is always a supra-anal opening.) 



■■ In Africa tlioro arc also Unioniila' of the subfamily Unioniriw; tiicN' uiiiloul>(edly point to a con- 

 nection with Asia, since such forms arc plentiful there, and (his indicates a different route of immigra- 

 tion from that of the Muleliiuv. 



^ The name depends upon the investigation of the anatomy of the .Vfrican genus Mutela, which is 

 unknown, but we have every reason to assume, chiefly through Von Ihering's study of the shell, that 

 this genus will fall under this family. The family name Mutdidw was first used by II. & A. Adams 

 (185S), but for an entirely different association of forms. The Mutdidw of .Simpson (1900) correspond 

 to our Muldinoi. 



