308 THE PEARLY FRESH-WATER MUSSELS— STMPSOX. 



VOL. XVIII. 



Grandidieria, Bourgiiignat, erected by that author into a genus, and 

 placed by him in the family Corbiculida',^ is merely a section of small, 

 rather solid, intlated Central African Unios, often having compressed, 

 reflected, dentate cardinal teeth, much like those of Unio parvus and 

 its allies of the United States. In 1888 Bourguignat claimed to know 

 twenty-five species of this genus in Lake Tanganyika, and believed 

 that if its waters were to be fully explored the number would be 

 increased to one hundred. No further comment is needed on the work 

 of the great master of the new school of French conchologists. 



Pharaonia, Bourguignat,- is another of this author's African genera, 

 which includes a few thin- shelled Unios, with compressed, elongated 

 cardinals and laterals. 



R(M€Us, Jousseaume,^ is still another so called genus, consisting of a 

 few small, thin-sbelled, concentrically-striated tropical African Unios. 



Microdontia, Tapperone Canefri,^ was established for Unio anodonti- 

 formls, Tajiperone Canefri, from the Fly River, New Guinea, and is 

 probably only a section of Unio. The very brief Latin description is 

 wholly inadequate for its proper determination. 



The characters of the shell and soft parts of the genus T^nio may be 

 summed up as follows: 



Shell variable in f<n-m, usually equivalve and inequilateral, rounded, 

 elongated, angular or symphynote; with tubercular, zigzag, or cou: 

 centric sculpture; beaks variously sculptured or smooth, and occasion- 

 ally showing vestiges of a glochidium; epidermis thick, hinge line 

 incurved in front of the beaks; hinge having normally one cardinal and 

 one lateral tooth in the right valve, and two cardinals and two laterals 

 in the left, or they may be almost whollj^ lacking or greatly varied in 

 arrangement: pallial line entire; interior nacreous. Animal di(ecious; 

 mantle open ; branchial opening oblong, fringed with numerous j)apill<e ; 

 anal opening with or without papilhe, usually separated from the 

 sujieranal opening; labial palpi generally wider than long, with free 

 points, more or less united posteriorly; branchi;e large, the embryos 

 being borne in the outer or inner pair, or rarely in all four of them. 



Genus BURTONIA, Bourguignat. •' 



I am inclined to believe that the species of this genus, of whose 

 anatomy nothing whatever is known, are merely peculiar, compressed, 

 somewhat symphynote Unios. In such species as I have been able to 

 examine, there are vestiges of cardinal and lateral teeth; the anterior 

 cicatrices are united, and the nacre is of a peculiarly rich, usually red- 

 dish tint. 



' Bull. Soc. Malac. France, II, pp. 1-12, 1885. 

 - Bull. Soc. Zool. France, XI, pp. 471-502, pi. xii-xiv, 1894. 

 3 Bull. Soc. Zool. France, XI, pp. 481, 482, pi. xii, Hg. 4, 1894. 

 ^ Ann. Mus. Genova, XIV, p. 229, pi. xi, tigs. 3-5, 1883. 

 5 Moll. Fluv. Nyanza, pp. 20-23, 1883. 



