PROCEEDINGS OF THE NATIONAL MUSEUM. 307 



have been subjected to injurious intiuences in the matter of food, dele- 

 terious water, or the like, until these characters have become more or 

 less fixed. In every group of Unios to which these Margaritauas seem 

 to belong, there are species in which the lateral teeth are more or less 

 imperfect, which seems to show that they have been somewhat suscep- 

 tible to these injurious influences. 



In view of the facts I have presented, and many others that might be 

 brought forward, I am forced to the conclusion that the so-called genus 

 Mar{/ari tana consists of a number of species of Unios with depauperate 

 cardinal or lateral teeth, or botli, and that they will have to be placed 

 in the genus U)iio. 



In southeastern Asia and some of the islands of the East Indian 

 Archipelago there is a peculiar group of Xaiades with greatly compressed, 

 somewhat elongated shells, having slightly concentric sculpture, the 

 species of which are almost or quite destitute of teeth, and have won- 

 derfully brilliant, silvery, soft- tinted nacre. This group consists of 

 probably but two or three species, though they have received a large 

 number of names, and is fairly typified by a form which Deshayes and 

 Julien called Anodonta sempervii^ens. jS^early all the specimens of the 

 different species show, when examined with a glass, long, delicate, 

 rudimentary laterals, and often vestiges of cardinals in the shape of a 

 smooth, compressed elevation. One of these Lea named MonocondyUva 

 compressa. They do not in any way ap^iroach any Anodonta I know of, 

 though most of the so-called species have been placed in that genus. 

 Deshayes and Julien' state that the animal is pure, milky white, but 

 that they "cannot give a detailed description of it, though it resembles 

 in its characters generally that of the species (of Anodonta) common 

 in streams and ponds." They appear to be most nearly related to 

 Unio semialatu.s, Deshayes, and others of the Mar(/inalis group. 



Rochebrune in 1882 ■^ gave the generic name Harmandia to Unio som- 

 horiensis, liochebrune. It is merely a peculiar Unio, having the surface 

 covered with somewhat radiating, sometimes slightly zigzag ribs, those of 

 theposterior running nearly horizontal, the remainder moreor less radiant 

 from the umbonal region. Near the center of the disk, two or three of 

 these irregular ribs before, and as many behind, curve toward each other 

 and join, somewhat after the manner of several South American species. 

 Sculpture api^roaching this, but not so strongly developed, is often found 

 in U. cceruleus and other Indian Unios. The laterals are double in each 

 valve, and a small, thin lamella curves upward from the ui)per lateral 

 near its posterior end. A vestige of this third, upper, curving tooth is 

 found in U. fluctiger, Lea, said to come from Guiana, but undoubtedly 

 an East Indian species, and the same character is found in U. eris2)atiis 

 of Gould. 



1 Mollusques Nouveaux du Cambodge. Nouv. Arch, du Museum, Bull. IX, pp. 122, 

 123. 

 ^BuU. Soc. Philoni. (7), VI, pp. 45,46, pi. i, 1882. 



