NO. 1205. SYNOPSIS OF THE XAIADESSIMPSOX. 803 



lateral in the right valve and two in the left; beak cavities deep, com- 

 pressed; nacre lurid; palleal line showing a slight posterior sinus. 1 



(Type, 1'iiio rttdnloxus Drouet and Chaper.) 

 tQUADRULA RADULOSA Drouet and Chaper. 



*Unio radnlosus DROUET ami CHAPEK, Mem. Soc. Zool. Fr.. V, 1892, p. 150, pi. v, 

 figs. 10-12. *J1. cle Conch., XLI, 1893, p. 41. 



tQUADRULA RADULOSA var. RHOMBOIDEA Simpson.- 



Borneo. 



The relationship of the following is uncertain. 



UNIO NEWENHUISI Schepman. 



* Unio newenhuisi SCHEPMAX, Notes Leyd. Mus., XX. 1898, p. 92, pi. i. figs. 1, 2. 

 * DROUKT, Jl. de Conch., 1899, p. 406. 



Borneo. 



May be related to Unio radulosus Drouet and Chaper. 



Genus SHISTODESMUS Simpson, 19OO. 

 (Type, I'nio lampreyanits Baird and Adams.) 



Shell rather solid, triangular, inflated, truncate above in front, some- 

 what swollen just behind the center of the base, pointed behind; beaks 

 high; beak sculpture not seen; surface thrown up into strong, very 

 wide, concentric ridges, one or two with each season's growth, and 

 pinched up in the central part to form a radiate row of compressed 

 knobs or spines; epidermis shining, greenish-yellow or brownish, having 

 marvelously delicate, concentric, microscopic lirre, often painted with 

 a few elegant, broken, green rays; there is one large, high, triangular 

 pseudocardiual in the left valve under the beak, a deep, triangular pit 

 in front of it, with an erect, radial lamellar tooth in its center, and a 

 high, lamellar, curved tooth in front of the pit, parallel with the edge of 

 the shell connected with the central tooth. A heavy triangular bifid or 

 trifid pseudocardinal in the right valve stands close to the anterior 

 edge of the shell and is separated from it by a deep, compressed pit; 

 behind this tooth, deep down at its base, is a narrow shelf, and back of 

 this the entire hinge plate is cut out in a deep sinus to the beak; two 

 laterals in each valve; cavity of the beak in left valve deep, somewhat 

 compressed; in the right entirely opened by the sinus; muscle scars 

 small, deep, smooth; pallial line with a sinus at its posterior end; a 



1 1 know nothing of the anatomy of this curious Xaiad, which seems to show 

 some relation to such species as Quadruhi microstictus and related forms. I place 

 it in Quadrula with doubt. 



2 There is a specimen in the U. S. National Museum marked Unio radulosus Drouet 

 and Chaper, from Borneo, which is quite rhomboid and but slightly sculptured on 

 the body, though it is plicate behind, which may bear the above name. It is prob- 

 ably a valid species. 



