93 



altera tribns : intus argentata, ad limbum nigra ; cicatricibus pro- 

 fundis. Long. |- ; alt. f poll. San Francisco, MaJ. Rich. 



A very curious species, clustering on sea-weed in the most 

 crowded manner, so that two adjacent specimens sometimes 

 wear each other nearly through, from friction in opening and 

 shutting. This circumstance, with the strong hinge and deep 

 cicatrices, show that the specimens are mature. The byssus is 

 coarse, wax yellow. 



Lima tetrica. T. solida, oblique ovato-triangularis, albida, 

 costis radiantibus ad 18 squamis semi-erectis posticis longioribus 

 armatis, horrescens ; apicibus acutis, elevatis, remotis, muricula- 

 tis ; marginali byssali rectilineari, hianle ; area cardinali lata, 

 valida ; fovea ligamentali minime profunda, costa transversal! 

 suffulta. Long. IJ- ; alt. 1^ ; lat. ^ poll. Gulf of California, 

 La Paz. Maj. Rich. 



Compared with L. squamosa, it is narrower and more com- 

 pressed ; the dorsal and ventral margin is less broadly rounded ; 

 the scales are more crowded, twice as long, inflexed at their 

 points, and much more developed at the dorsal margin ; there 

 are no stria3 on the dorsal area. The remarkable brace or rib 

 under the ligament pit, by which a deep cavity at the apex is 

 formed, is remarkable, but possibly accidental. 



AvicuLA STERNA. T. soUdula, badia radiis pallidis ornata ; 

 epidermidc cinereo serratim fimbriate induta ; apicibus ad quad- 

 rantem anteriorem positis ; ala semicirculari, modice obliqua, 

 declivitate umbonali tumido, abrupto ; cauda longissimia, gra- 

 cili ; auriculis magnis, radiatim striatis ; fissura byssali profun- 

 dissima, acutangulari : margarita argentata, valde iridescens ; 

 limbo fusco-marmorato. Long. 2^ ; lat. 1| ; alt. f poll. In- 

 habits Mazatlan. Lieut. Green. 



Has the general appearance of A. semisagitta, but the wing is 

 less oblique and curves directly into the cauda without any sinus ; 

 the byssal sinus is deeper and much more acute, making a trape- 

 zoidal auricle. The cauda is much shorter in A. Tarenlina and 

 the wing much more oblique. It most nearly resembles a Flo- 

 rida species, but in that the byssal angle is obtuse, the auricle 

 triangular, the cauda shorter. 



