UNTO.— Plate LXXXI. 



The primary teetb appear from the drawing to be trian- 

 gular, and by no means small ; they are stated, however, 

 to be rather small, depressed, and striated. 



Species 429. (Mus. Lea.) 



Usio CouCHlANUS. Un. tedd quadraid, inflatd, crassd, in- 

 aequilateraU, aniice rotunda, posfice biangulaid, lav/, 

 oUvaceo-fusen, concolore, ante costam mnhonttlem, 

 latum, et angulaiam radialim excavatd, pone earn 

 planidatd et, coMpiciie olAiqiie xulcatd ; margine iieii- 

 trali aiitice arcuato, positce emarijinato ; natihiis emi- 

 nenfibus, lunidd conspiciid, margaritd albidd; denti- 

 bus cardinaUbiis subgrundibm, erecth, riigosn-itriatis, 

 crenulatls ; de/Ulbas lattralibui >iiiblo)igis, cras-iis, sub- 

 arcuatis. 



t'oucu's Unio. Shell squarish, inflated, thick, inecpii- 

 lateral, rounded in front, bianjTulated behind, smooth, 

 of an uniform olive-browu, with a ray-like hollow 

 before the broad and angular uraboiial ridge, flat- 

 tened and with conspicuous slanting grooves behind 

 it ; ventral edge arched in front, emarginated be- 

 hind ; nacre vvliitish ; primary teeth rather large, 

 erect, rugosely striated, crenulated ; lateral teeth 

 somewhat long, thick, rather curved. 



LfcA, Proc. Ac. N. S. Philad. 1S60, p. 305; Obs. on 

 Unio, vol. viii. p. 53. pi. 06. f. 196. 



Hub. Eio Salado, New Leon, Mexico. 



The contrast between the coarse fold-like appearance 

 of the broad flat posterior dorsal slope and the general 

 smoothness is very striking. 



Species 430. (Copied from Lea.) 



Unio Popei. Un. testa elongatd, xubtenui, depresm-ci/- 

 I'mdraced, ivferne return, antice angustd et porrectd, 

 postici^ proditctd et subtrtmcato-biangnlatd, fused ant 

 olivaced, obsolete radlatd, Irgvignfd; uatibics pai'vis, 

 proiiiiiinlii, ad apices granidatis, margarita albd, 

 mnniinqiimn paUidi aurantio-rubrd ; dentibM cardi- 

 nalibtis compressis, erectis, aciiminatis, cretiidatis ; 

 derdibas lateralibus prcelongis, lamellatis, suhrectis. 



Pope's Unio. Shell elongated, depressed-cylindrace- 

 ous, indented ventrally, narrow and projecting in 

 front, produced and subtruncately bianguiated be- 

 hind, brown or olive, with indistinct rays, smooth ; 

 beaks small, rather prominent, granulated at the 

 tips ; nacre white, sometimes salmon-coloured ; pri- 

 maiy teeth compressed, erect, acuminate, crenulated ; 

 lateral teetli very long, lamellar, nearly straight. 



Lea, Obs. oq Unio, vol. viii. (Journ. Ac. N. S. Philad. 

 ser. 2. vol. iv.), p. 54. pi. 60. f. 197. 



Hnb. Texas, and New Leon in Mexico. 



Lea remarks that the posterior slope is raised iuto a 

 carina, and is rayed with two impressed lines. 



