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TRAPEZOIDEUS. 195
320. Trapezoideus exolescens {Gould).
Trapecoideus exolescens (Gould); Simpson, Washington, D.C,
Smiths. Inst., Nat. Mus. Proc. xxii, 1900, p. 859.
Unio exolescens, Gould, Proc. Boston, Soc. Nat, Hist, i, 1843,
p. 141 ; Catlow & lleeve. Conch. Norn. 184S, p. 59; H. &
A. Adams, Gen. Eec. Moll, ii, 1857, p. 493: H. & T., 0. I.
1876, p. 43, pi. 107, fig-. 5; Pretel, Conch. Sam. iii, 1890,
p. 152,
Margaron (Unio) exolescens, Lea, Sjn. 1852, p. 32; 1870, p. 51.
Original description:—Testa transvei-so-oblongata, inequilaterali,
subcompressa, fusco-virescente ; postice dilatata, sub-biangulata ;
umbonibus subelevatis; dentibus cardinalibus parvis, obliquis,
interdum exoletis; lateralibus remotis, reotis; margarita livida
vel ferruginea.
Long. 32, ]at, 70, diam. 15 mm.
Hah. Tavoy ; also Bhamo (Indian Museum Collection).
321. Trapezoideus theca (Benson).
Trapezoideus theca (Benson) ; Simpson, Washington, D.C, Smiths.
Inst., Nat. JIus. Froc. xxii, 1900, p. 859.
Unio theca, Benson, A. M. N. H. x, 1862, p. 186; II. & T.,
C. I. 1876, p. 6, pi. 12, fig. 5; Pa3tel, Conch. Sam. iii, 1890,
p. 169.
Original description:—Testa transverse oblongo-ovata, valde
insequilaterali, tenui, compressa, antice et postice rotundata,
superne subtusque convexiuscula, margine ventrali medio recto;
disco subplanato, IsBviusculo, lineis transversalibus subrugosis'
versus margines notato ; epidermide pallide stramineo-lutea;
umbonibus planatis, decorticatis, versus apices tenuis prominulos,
concentrioe sulcatis, postice lineis duabus radiantibus tenuibus
sabelevatis munitis; ligameiito longiore; dentibus cardinalibus
laminatis, tenuibus, brevibus, utriusque valvsB duplieibus, valvie
dextrse prope marginem anteriorem sitis, obliquis; sinistra lobo
subapicali transverse, anteriore obliquo, lateralibus elongatis, vix
curvatis, valvse dextrre simplicibus, sinistrse duplieibus ; margarita
lutea, versus marginem ventralem albida.
Long. 20, lat. 40, diam. 10 mm.
Hah. Eiver Cane, near Banda, Bundelkhund.
The above description is amplified by the following notes :—
"Interior of shell transversely subplicate; cavity of beaks
shallow. Anterior cicatrices separate, posterior confluent, apical
ones in the cavity of the beaks. Some slight rugse are visible on
the posterior slope at right angles to the strise of growth.
" The shell is somewhat wider posteriorly than
anteriorly. The pale opaque straw-colour of the unpolished
epidermis is also a peculiar feature, not observable in any other
Northern Indian species.
the double umbonal line, apparent occasionally in adult
specimens of U. [(L.) L.] marginalis, is conspicuous."
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