UNITED STATES AND NORTHERN MEXICO -11 



straight; anterior cicatrices small, distinct and well impressed; posterior cicatrices 

 nearly distinct and very sliglitly impressed ; dorsal cicatrices situated under the plate 

 immediately above the centre of the cavity of the beaks ; cavity of the shell moder- 

 ately deep and wide; cavity of tlie beaks deep and anjinlar: nncro jmrplisli and very 

 iridescent. 



Rema7-lcs. — A single specimon only of this interesting little species without the soft 

 parts, was obtained by Major LeConte. It is remarkable for its quadrate outline and 

 flattened side, reminding one of a large bean of the Theohroma cacao or common coco. 

 It inclines also to that shade of brown in the epidermis, but is rather more chestnut 

 brown. In outline it very closely approaches U. mode-itus, Fer. ; but that species 

 which comes from Brazil has a blackish epidermis and a white nacre, and it is rather 

 smaller, thinner and higher on the posterior slope. The cacao has some resemblance 

 to ^vcctfssus (nobis), but that species is rotundo-trinnG:nlar, and rather larger in the 

 elevation of the posterior slope. 



Unio ungu^formis. pi. 50, fig. 170. 



Testa loevi, elliptiea, compressfi, ad latere planulata, infcquilaterali, postict' obtuse biangulata, antice rotun- 

 (lata; valvulis subtenuibus, antico crassioribus ; natibus prorainulis; epiderraide palliJo-luteri, subnitiJa, 

 virido-radiatiV ; dentibus cardinalibus parviusculis, obtuso-conicis, crenulatis, in utroque valvulo dupli- 

 cibus; lateralibus sublongis, lamellatis subcurvisque ; margarita alba et valde iridescente. 



Shell smooth, elliptical, compi'essed, flattened at the sides; inequilateral, obtusel}'^ 

 biangular l)ehind, rounded before ; valves rather thin, thicker before ; beaks slightly 

 prominent ; epidermis pale yellow, somewhat shining, with greenish rays ; cardinal 

 teeth rather small, obtusely conical, crennlate and double in both valves ; lateral 

 teeth rather long, lamellar and slightly curved ; nacre white and very iridescent. 

 Pi-oc. Acad. Nat. Sci. 1860, p. 305. 



Hah. — Colnnil)ns, Georgia, Dr. Boykin; rmd French Broad River, Tennessee, Dr. 

 Edgar. 



My cabinet. 

 Diam. -6, Length 1-1, Breadth 2 inches. 



Shell smooth, elliptical, compressed, flattened at the sides, inequilateral, obtusely 

 biiingular behind and rounded before; substance of the shell rather thin, thicker 

 before; beaks slightly prominent; ligament rather short, somewhat thick and dark 

 brown; epidermis pale yellow, somewhat shining, with greenish interrupted rays over 

 the posterior and middle portions of the disk, and with rather distant marks of 

 growth; umbonial slope slightly raised and somewhat flattened ; posterior slope some- 

 what carinate and with a slightly impressed rather broad groove which causes an 

 emargination on the posterior superior margin ; cardinal teeth rather small, obtu.sely 

 conical, crennlate and doiil)le in both valves, but slightlv so in the left; lateral teeth 



