1895. 



PROCEEDINGS OF THE NATIONAL MUSEUM. 323 



region. The embryo, as v. Iheriug has shown, is a lasidium. By the 

 characters of the shell most of the Glahnris are closely rehitod, and v. 

 Ihering has placed these two species in tlie same gronp. Here, tlien, 

 in another genus, is an example of the great variation of siphonal 

 development in closely related forms, which helps to prove that the 

 character is not constant. Dr. Lea found that in G. (ri/mani, Lea, and G. 

 l((to-marginata. Lea, the branchiiv were united their whole lengtli to the 

 ab<lominal sac, and the palpi of both were rounded, and he stated that 

 in this latter respect they differed from all N^orth American Anodontas 

 he had examined. Tlie superaual opening was not united below. And 

 in Glabaris streheli, Lea, of Mexico, which is closely allied to the South 

 American forms, he found the same kind of rounded i^alpi which were 

 united only above. The genus is distributed from central Mexico all 

 through Central and South America to Patagonia, but has not been 

 found west of the Andes, though a number of Unios are met with in 

 that region. 



Genus LEILA, Gray.' 



Conchologically Leila is very close to Glabaris. The color, form and 

 texture of the shells are the same as in species of the Trapezialis group 

 of Glabaris. and, like most of those forms, they gape more or less in 

 the anterior ventral region. According to von Ihering Leila has siphons,^ 

 and the pallial line in most specimens is quite deeply and broadly 

 indented in the siphonal region. But the latter character is often found 

 in a less degree in the shells of Glabaris trapezialis and its allies, espec- 

 ially G. sinuata and G. anserina. Both Jjeila esula and L. blainvilleana 

 occasionally show vestiges of taxodont teeth near the beaks. The 

 range of the genus is much the same as that of Glabaris, but I do not 

 know of its having been found in North America. 



Genus MONOCOND YL^^A, d'Orbigny.'' 



This group was first described as a subgenus of Unio, and was 

 afterwards given generic rank in the author's great work on the mol- 

 lusks of South America. 



Sjiix's name, Aplodon,* was preoccupied by Eafinesque, in Heliacea 

 in 1819, and therefore it must be relegated to the synonymy. 



The shells of this group are generally solid, with a rather rough, 

 brownish or greenish, cloth-like epidermis. The right valve has a large 

 tooth opposite the beak, and a smaller one some distance forward of it. 

 The large tooth of the left valve fits the space between, and there are 

 occasionally small scattered denticles on the hinge plate. According 

 to d'Orbigny,^ Moiiocondyhca gitarayana, d'Orbigny, has long, rounded 



'Syu. Brit. Mus., 1840, p. 142. 



2Zool. Anzeiger, Nos. 380, 381, p. 2, 1891. See also Fischer, Man. de Conch., p. 1005. 



Hiuer. Mag. Zool. CI., V, No. 62, p. 37, 1835. 



"Test. Fluv. Braz., pi. xxv, figs. 1, 2, 1827. 



^Voy. Amer. Mer., pi. Lxviii, fig. 7. 



