TRAPEZOIDEUS 1 1 85 



Trapkzoideus ExoLi^scENs (Gould j. 



Shell long rhomboid, inequilateral, rather thin, subconi- 

 pressed ; anterior end rounded, narrowed ; dorsal outline lightly 

 arched ; dorsal slope obliquely truncate ; base line nearly 

 straight ; posterior ridge double, ending in a feeble biangula- 

 tion near the base ; surface with irregular, concentric sculpture, 

 and in some cases faint plications on the dorsal slope; epider- 

 mis smoky-brown ; pseudocardinals rather shorter than in most 

 of the species, feebly developed ; laterals remote, well devel- 

 oped ; nacre bluish, lurid purplish in the cavities. 



Length 69, height 32, diam. 17 mm. 



Tavoy, Burma. 

 Unio exolescens Gould, Pr. Bost. S. N. Hist., I, 1843, p. 141. — 



Hanley and Theodald, Conch. Ind., 1876, p. 43, pi. cvii, 



fig- 5- 

 Margaron (Unio) exolescens Lea, Syn.. 1852, p. 2)2 '■> 1870, 



P- 51- 



Trapezoideus exolescens Simpson, Syn., 1900, p. 859. 



Four odd valves are in the Lea collection, presented by Dr. 

 Gould under the name Unio exolescens. It is quite a distinct 

 species, differing from others of the group in its dark epider- 

 mis, the color of its nacre and the shorter pseudocardinals. 



Trapezoideus theca (Benson). 



Shell rather small, scarcely subsolid, somewhat elongated, 

 subrhomboid. quite inequilateral, beaks small but somewhat 

 sharply elevated : anterior end narrowed, a little, rounded ; base 

 line a Httle inflated just behind the middle ; dorsal outline nearly 

 straight ; outline of dorsal slope obliquely rounded ; posterior 

 ridge rounded ; surface with rather strong concentric sculpture 

 and slightly corrugated ; dorsal slope plicate ; epidermis yellow- 

 ish ; teeth delicate ; pseudocardinals oblique ; nacre bluish, red- 

 dish in the cavities, iridescent. 



Ivcngth 40. height 21 mm. 



Cane River, Bundelkhund, India. 

 Unio theca Benson, Ann. and Mag., X, 1862, p. 186. — Han- 



LEY and Theobald, Conch. Ind., 1876, p. 6, pi. xii, fig. 5. 

 Trapezoideus theca Simpson, Syn., 1900, p. 859. 



