THK NAUTILUS. 51 



lamelliform. I believe the L. sapperi more allied to L. umbrosus 

 Lea than to explicates, being, however, of a more elongate form with 

 produced posterior extremity and larger size. The type example has 

 a length of 64 mm., breadth of 114 mm., diam. of 38 mm. The 

 epidermis is dark brown, blackish, the nacre white. The posterior 

 slope has two obtuse, somewhat indistinct diverging lines. The spe- 

 cies is from the Chixoy river in Guatemala, and dedicated to Dr. 

 Carl Sapper, who has collected in scientific expeditions in Central 

 America and Mexico many interesting Unionidce, for which I am 

 much indebted to him. 



Nephronaias medellinus Lea seems to be the same as Lampsilis 

 aztecorum Phil. 



Nephronaias averyi Lea, I have from the Rio Tuca, in N.-W. 

 Guatemala. 



Nephronaias goascoranensis Lea (1858), I have received from 

 Dr. Sapper from the Moramusko river, in Honduras, and from the 

 Rio Coco in Nicaragua. The species varies, and I have specimens 

 corresponding to the figure of Lea and others to that of Crosse and 

 Fischer (Miss. Sci., Mexico, pt. 2, 1894, pi. 64, fig. 5 and 5 a), of 

 Unio calamitarum Morelet (1840.) The name of this widely- 

 distributed Central American species should, therefore, be Nephro- 

 naias calamitarum Morelet, if Morelet, as also Crosse and Fischer 

 have not confounded two different species, and it is impossible to 

 say what is the true calamitarum. 



Nephronaias tabascoensis Kuster (1856) is also a widely-distributed 

 Central American species. This is my No. 60 from the Rio Copan, 

 Guatemala, tributary of the Motagua river, and which Mr. Simpson 

 believed be the scamnatus Morelet. Having both N. scamnatus 

 Morel, and gandlachi Dunker from Cuba, I consider them different. 

 The true scamnatus is a smaller and thinner shell, while to tabasco- 

 ensis are synonymous U. persulcatus Lea, rugulosus Kiist. and per- 

 haps also plicatulus Kuster. To this species belongs also Unio cala- 

 mitarum Morelet, var. prolong ata Crosse et Fischer 1. c, p. 612, pi. 

 63, fig. 5 et 5 a. The supposed Central American examples of N. 

 scamnatus may be identical with N. dysoni Lea. N. tabascoensis I 

 have also from Nicaragua, Rio Telpanek, and (No. 61) from El 

 Obrage, Guatemala. 



Referring to the genera of North American Unionidae admitted 

 by Simpson, I would make the following observations: 



