166 



NATURAL HISTORY OF VERMONT. 



Part I. 



FRESH WATER AND LAND SHELLS. 



posterior margin descendins^ obliquely in 

 a straight or slightly curved line, rounded 

 below ; inferior margin slightly curved ; 

 anterior margin regularly rnanded ; inner 

 surface bluish, sometimes with a light sal- 

 mon-colored nacre anteriorly or through- 

 out. Dimensions of two specimens : No. 

 1, length 2.2 inches; height 1.4 inch; 

 width 1.06 inch. No. 2, length 2.0(5 inch- 

 es ; height 1.2 inch ; width O.'J inch. 



Remarks. — This species is rather com- 

 mon in the northern middle states. — 

 When young the epidermis is of a ligliter 

 color, the rays are more conspicuous, and 

 the shell is shining and beautiful. 



Genus Unio. 

 Generic Clifiracters. — Shell as in Alasmo- 

 donla, bill is also fiirnislicd with very long lanu.ilar 

 lateral jios:erior tt-eth, u.«ualiy oiio on (he rigiil 

 valvfi fnterin<» heiweon two on llie |i-ft. Very 

 rarely the riglil valve has one eiitcrini; belvveen 

 two on the left. The cardinal leetli are oflen 

 double, sometimes Irijilc. Animal as in Anodon- 

 ta. 



Unia alalus. — Sav. 



Description. — Shell ovate-triangular, 

 moderately thick ; epidermis olive, or 

 brownish green, with numerous fine and 

 some coarse striae of growth ; bqaks small, 

 not prominent, in the young shell exhib- 

 iting small wrinkles; discs moderately 

 inflated posteriorly, compressed anterior- 

 ly, with one or two .small posterior angles 

 above ; anterior side small, one-fourth to 

 one-fifth as long as the posterior ; hinge 

 margin straight, very much elevated be- 

 hind into a triangular connate wing, the 

 posterior mnrgiu of which is incurved; 

 the remainder of the posterior and the an- 

 terior margins are regularly rounded ; in- 

 ferior margin nearly straight ; inner sur- 

 face usually purplish red, rarely very pale 

 red, sometimes of a rich reddish salmon 

 color; cardinal teeth rather small. Di- 

 mensions of two specimens: No. 1, length 

 5.3 inches ; height 3.8.5 inched ; width 1.75 

 inch. No. 2, len'-rth 5.9 inches; height 

 3.85 ; width 2.2 inches. 



Remarks. — No. 2 is a very old shell. 

 In such the wing is nearly obsolete, and 

 consequently the form is more ovate. 

 This species is very abundant in Lake 

 Champldin, east of which it has never 



been found. In the western states it is 

 common. 



Unio gracilis. — Barnes. 

 Descrittion. — Shell ovate-triangular, 

 rather thin ; epidermis straw-color, coarse- 

 ly striate near the margins, otherwise 

 smooth and shining; beaks small, not 

 prominent, smooth ; discs considerably 

 inflated, convex, with two or three slight 

 ridges jjroceeding jiosteriorly above ; an- 

 terior side small, compressed, about one- 

 third as long as the posterior; hinge mar- 

 gin nearly straight, much elevafed poste- 

 riorly into a triangular connate winor, of 

 which the posterior margin is incurved ; 

 other margins regularly rounded, the ba- 

 sal moderately ; inner surface iridescent, 

 bluish, pink above ; cardinal teeth very 

 small. Length 5 inches; height 3.5 inch- 

 es ; width 1.6 inch. 



Remarks. — This species has the form 

 and size of the preceding, but is easily 

 distinguished by the color of the epider- 

 mis, of the nacre, greater inflation, and 

 thinness. It is common in lake Ciiam- 

 plriin, and, like U. uLatus, is not found 

 any farther to the eastward, but is com- 

 mon througii the western states. 

 Unio comjjrcssns. — Lea. 

 Description. — Shell oblong-ovate, not 

 thick ; epidermis grass-green, or oliva- 

 ceous, with numerous irregular yellowish 

 rays, with distinct stria; ; beaks small, 

 pointed, much wrinkled ; discs moderate- 

 ly intiatcd posteriorly, scarcely convex; 

 anterior side three-sevenths to three- 

 eighths as long as the posterior; hinge 

 margin straight, rising posteriorly into a 

 slightly elevated wing, which is oflen 

 more or less connate; posterior margin 

 descending obliquely in a straight line to 

 a somewhat rounded truncate extremity; 

 inferior margin somewhat rounded ; an- 

 terior margin regularly rounded ; interior 

 bluish, sometimes tinged with pale brown- 

 ish yellow ; cardinal teeth much com- 

 pressed, on the left valve deeply and 

 broadly bifid, or even trifid ; of the lamel- 

 lar teeth of the left valve one is very 

 small. liCiigth 2. 85 inches; height 1.6 

 inch ; width 0.8 inch. 



Remarks. — This species also is found 

 in the western states, and has its eastern 

 limit in the streams west of the Green 

 Mountains. It is much larger in the 

 west. 



Var. ■plebeius. — Adams. Epidermis oli- 

 vaceous, ra)^s obscure ; wing scarcely ele- 

 vated ; lamellar teeth very small, with 

 the three divisions of the left cardinal 

 very remote. Length 4.3 inches ; height 

 2.3 inches; width 1.25 inch. This va- 

 riety is found in a small brook in Middle- 

 bury. 



