140 MAZATLAN BIVALVES 
191. Byssoarca Fusca, Brug. 
Arca fusca, Brug. Dict. no. 10.—D’ Avila, Cat. vol. i. pl. 7, 
f. R.—Hneycl. pl. 308, f. 5.— Dillw. Cat. vol. i. p. 231, 
no. 14.—Lam. An. s. Vert. vol. vi. p. 466, no. 14.— Rve. 
Conch. Ic. pl. 12, f. 82.—B. M. Cat. Cuba Moll. p. 43, no. 528. 
Arca barbata, var. Gmel. p. 3307.—Schrot. Einl. vol. i. p. 279, 
no. 2.—List. Conch. pl. 231, f. 65.—Gualt. Test. pl. 90, f. B— 
Chemn. Conch. vol. vii. pl. 54, f. 534. 
Area bicolorata, Chemn. Conch. vol. xi. p. 243, pl. 204, f. 2007.— 
Dillw. Cat. vol. i. p. 230, no. 11. 
The presence of this well-known East Indian shell in the 
Mazatlan fauna is very suspicious. I took one fresh pair, and 
Mr. Darbishire another, out of the Byssoarca box, when I first 
examined the Collection. As it is said to reach the West In- 
dies, it may linger also in the Gulf seas; or these specimens 
may have come over on ship bottoms or drifting timber, or in 
ballast ; or they may, in some unaccounted way, have found 
an entrance into their appropriate box by an accident of the 
owner’s. A small oyster attached is not distinguishable from 
the Mazatlan species; but this does not prove much. Long. 
1°24, lat. 1°98. alt. °97. 
Hab.—Madagascar and Barbadoes, Lamarck.—‘‘Singapore,” 
abundant, P. P. C.—Barbadoes, (young valves) °P. P. C— 
Cuba, Sagra.—Mazatlan: extremely rare; L’pool Col. 
Tablet 650 contains the specimen I found. 
192. ByssoaARCA VESPERTILIO, 2. s. 
B.t. oblonga, compressa, posticé tuinidiore, expanst ; valde 
inequilaterali, marginibus subrotundatis, hiatu pedis modico, 
margine tht incurvo ; umbonibus subappressis, ligamento longo, 
ngusto, antice brevi; superficie radiatim striata, striis swb- 
tmpressis, lineis incrementi vix decussatis; rubro- 
fusca, intus maculis duabus ab umbonibus radiantibus ; epider- 
mide lamellis concentricis, antice squamosis, postice brevibus 
setis interstitia decurrentibus, in lamellis imbutis; hue 
et illuc lineis setarum validis, longis, maxime latere postico, 
ubi semitubulares sunt; dentibus haud parvis, haud 
numerosis, lineis valde incurvatis, anticd brevi. 
Compare A. setigera, Rve. Proc. Zool. Soc. 1844, p. 124; Conch. 
Ie. pl. 14, f. 94. (Zanzibar, under stcnes at low water, Thorn.) 
