THE NAUTILUS. 



25 



Later (NAUTIL 31.' 17 p. 47) he distinguishes as Nephronaias 

 '(s. s. ) a group of species, containing plicatulus, persulcatus, 

 melleus, dysoni, ortmanni, ravistellus etc., of which he says that 

 the anatomy resembles that of EUiptio, but that it " differs from 

 EUiptio in its sulcated disk, in its beak sculpture etc." But it 

 should be remembered that only the anatomy of ortmanni was 

 known. 



My own determination of the genus Nephronaias (Ann. Cam. 

 Mus. 8. '12 p. 326) rested upon the examination of the soft 

 parts of N. sapotalensis(Leei), which surely is a Lampsiline shell ; 

 but I have pointed out that it is all important to determine the 

 position of the type species of the genus, Unio plicatulus Charpen- 

 tier. Frierson now assumes, from the characters of the shell, 

 that plicatulus, has the same anatomical structure as ortmanni. 

 This may be correct, but has not been demonstrated; but if 

 correct, the name Nephronaias becomes either a synonym of 

 EUiptio, or a subgenus of it, or a genus closely allied to it. 



In view of the great deficiency in our knowledge of the Mex- 

 ican and Central American species, I prefer, for the present, 

 to leave those species, which have EW/ptio-structure, in the 

 genus EUiptio. Of the following forms, the anatomy is more or 

 less known to me. 



ELLIPTIC ORTMANNI (Frierson) (1. c. ). 



Specimens, cotypes, from Rio Conchins, Quirigua, Guatemala, 

 have been investigated, collected Febr. 4 and 6, 1913. 



Frierson (1. c., p. 15) has already indicated the essential 

 features of the anatomy of this species. It should be added, 

 that the anal opening has crenulations, the branchial papillae; 

 that the mantle connection between anal and supraanal is 

 moderate (in most of my specimens torn by rough handling); 

 that the posterior margins of the palpi are connected for about 

 half of their length. The inner lamina of the inner gills is free 

 from the abdominal sac, except at its anterior end. The mar- 

 supium is in the outer gills, placentae are present, sublanceo- 

 late, not very solid. Marsupium moderately swollen, its edge 

 remaining sharp, when charged. Glochidium gubcircular, L. 

 0.23, H. 0.22 mm. Color of soft parts (in alcohol) pale. Male 



