UNITED STATES AND NORTHERN MEXICO. 10 



regularly rounded before and very inequilateral ; valves rather thin ; beaks slightly 

 prominent, minutely and regularly undulate at the tips; epidermis somewhat shi- 

 ning and covered with small rays; cardinal teeth small, crenulate and double in both 

 valves ; lateral teeth long, lamellar and nearly straight; nacre puri)le and very iridescent. 

 Proc. Acad. Nat. Sci. 1859, p. 154. 

 JIah. — Big Uchee River, Alifbama, near Columbus, Georgia. G. Hallenbeck. 

 My cabinet and cabinet of Mr. Hallenbeck. 

 Diam. -7, Length 1-2, Breadth 2.G inches. 



Shell smooth, broadly elliptical, compressed, flattened behind and obtusely angular, 

 regularly rounded before and very inequilateral ; substance of the shell rather thin, 

 very slightly thicker before; beaks slightly prominent, minutely and irregularly 

 undulate at the tips ; ligament rather long, somewhat thick and light brown ; epider- 

 mis somewhat shining, thickly covered with small green rays over the whole disk, 

 with rather distant marks of growth ; umbonial slope very slightly raised and very 

 obtusely angular ; posterior sloj^e very narrow, carinate, with two slightly impressed 

 lines and usually with well marked yellow and green rays from the beaks to the pos- 

 terior margin; cardinal teeth small, crenulate, striate, and double in both valves; 

 lateral teeth long, lamellar, enlarged towards the posterior end and nearly straight ; ante- 

 rior cicatrices distinct and well impressed ; posterior cicatrices confluent and slightly im- 

 pressed ; dorsal cicatrices placed immediately over the centre of the cavity of the 

 beaks; cavity of the shell very shallow and broad: cavity of the beaks very shallow 

 and rounded ; nacre purple and very iridescent. 



Remarhs. — Nearly a dozen si^ecimens are before me of different ages, but none were 

 received with the soft parts. This species belongs to the complanatm group, but it is 

 more transverse than that shell usually is. It also has a more lenticular aspect, the 

 greatest cross diameter being nearly in the centre of the disks. All the specimens 

 received have a purple nacre and this no doubt is the prevalent color, but still it may, 

 like complanatus, sometimes be found salmon color or white. It is somewhat allied 

 to salehrosus (nobis), but may easily be distinguished by its being of a more elliptical 

 outline, and in being usually darker in the epidermis and covered with capillary green 

 rays which cover the whole disk. The undulations of the beaks also differ. In the 

 virkUracliatus the anterior superior tractor muscle makes a cicatrix on the j'osterior 

 side of the great adductor, and in some specimens this cicatrix is quite separate, 

 leaving a small ridge between the two. 



Uxio viRiDANS. PI. 54, fig. 1G2. 



Testa laevi, oblonga, compress;!, ad latere planulata, postice biangulata, anticc rotundata, raldO inacquilater- 

 oli; valvulis subtenuibus; natibus prcminulis, ad apices undulatis; cpideniiide fusco-viridi, striata, ob- 

 Bolete radiata; dentibus eardinalibas parvis, striatis. crenulatis; lateralibus pnclongis, lamellatis, sub- 

 rectisque; margarita vel albu vel salmonia, srcpe purpurea et valde iridescente. 







I 



