5 
oblique furrow from a small oblique projec- 
tion remplacing the lamellar tooth, with a 
small fold in it. 
All these shells are transversal and ine- 
quilateral; I have seen none yet longitudinal 
as among the Unios: most of the species are 
ribbed behind. The A. complanata of Say, 
must form another peculiar Genus, which I 
propose to call Pterosyna ; having the united 
wings behind of the Genus Metaptera . The 
2 Alasmodon of my monograph belong to the 
G. Lasmigona . 
102 Sp. Alasmodon ponderosum , (Lasm. 
ponderosa, 1820.) Elliptical, very thick, 
somewhat swelled, truncate and broadly rib- 
bed behind: yellowish and laminated outside, 
white and uneven inside. Length 3-5, di- 
ameter 1-3, axis 1-3 of the breadth. 
In lower Ohio and in the Mississippi.-— 
Large heavy shell, five to six inches broad, 
roughly rugose outside by their concentric 
lamina. Cardinal tooth nearly trilobe, la- 
mellar angle obtuse, confluent together. 
If these characters of the teeth should 
separate it from the Lasmigona , it may be 
called Gonatnblus. 
103 Sp. Alasmodon rug o sum \_L. rugosa. 
1823.] Shell thick elliptical, hardly swelled, 
subtruncate behind, broad ribs behind and 
below, subsinuate below, outside rugose and 
olivaceous, white and nearly even inside. — 
Length 3-5, diameter 1-4, axis 3-4 of 
breadth. 
Tennessee river, rare, 5 to 6 inches broad. 
Akin to the last, but more flat, less thick 
and heavy, teeth different, cardinal smaller 
not trilobe, angular projection less obtuse, 
with a wrinkle and small tooth at the base. 
104 Sp. Alasmodon sulcatum , (L. Sulcata. 
1823.)* Shell thick, elliptical and swelled, 
posterior slope with broad ribs, surface oliva- 
ceous with large sharp concentric ribs and 
broad furrows between, inside white incar- 
nate. Length 1-2, diameter 1-3, axis 1-4 of 
the breadth. 
River Tennessee and Mississippi: fine 
large shell, 6 inches broad, beautiful nacre; 
cardinal tooth crenate, the angular projec- 
tion acute before, obtuse behind. Beak or 
apex a little prominent and slighty rugose. 
Very rare. 
105 Sp. Alasmodon viridis, (L. viridis 
disc . 1820.) Shell thin swelled, subelliptical 
quadrulated, posterior slope slanting truncate 
without ribs: outside greenish, nearly smooth, 
inside bluish, with flexuose wrinkles. Length 
1-2, diameter 1-3, axis 1-3 of the breadth. 
Var. I. Chloris. Bright green. 
Yar. II. Radiata. Olivaceous with green 
rays. 
Yar. III. Fuscata. Brownish. 
In the Ohio and other streams. So much 
like Unio viridis outside as to be easily mis- 
taken for it. Tooth small bilobe crenate, 
angular projection sharp with a wrinkle or 
furrow. One or two inches broad. 
5 N. G. Amblamodon. 
106 Sp. Alasmodon hians [Amblasmodon 
hians, 1823.] Shell thick, much swelled, el- 
liptical, subobliqual tfhd gaping, margin flex - 
uolate, posterior slope with broad ribs. Out- 
side rugose and yellowish brown, inside even 
pale incarnate. Length 7-20, diameter 2-5, 
axis 1-4 of length. 
River Tennessee, fine rare shell, 5 inches 
broad. Hinge quite peculiar, cardinal tooth 
not lobed, large subcrenate, large oblique 
knob on the projection decurrent, twisted and 
curved behind. 
6 N. G. Decurambis. 
107 Sp. A lasm. Scriptum ( Decurambis life - 
rata disc. 1822.) Shell rather thin, subellip- 
tical, very much swelled, truncate behind, 
nearly flat with transverse furrows and ribs, 
subsinuate beneath. Outside smooth green- 
ish with blackish spots like capital letters 
inside bluish. Nearly equilateral, apex ar- 
date. Length and diameter one half, axis 
5-12 of the length. 
In Green river. Wonderful shell, exceed- 
ingly rare and strange, outside form of a 
Truncilla , 2 or 3 inches broad. Tooth flex- 
uose trilobe compressed, decurrence befid be- 
fore. Certainly a peculiar genus. 
108 Sp. Alasm. atropurpureum (Decuram- 
bis, ditto, disc . 1823.) Shell rather thin, el- 
liptical, hardly swelled, smooth and not trun- 
cate behind* subsinuate beneath: outside 
rugose, blackish purple, quite inequilateral, 
apex hardly cordate. Length one half, diam- 
eter and axis one third of the breadth. 
In the river Cumberland, very rare, 3 
inches broad. Tooth flexuose subtrilobe, 
hardly prominent. Yery distinct from the 
last, although a true Decurambis. 
7 N. G. Sulcularia. 
109 Sp. Alasm. badium (Sulcularia badia 
disc. 1821.) Shell thin, suboval, truncate 
obliqually behind, back straight, rounded be- 
neath, outside smooth bay with some faint 
bands, inside pale bay or rufous iridescent. 
Length 2-3, diameter and axis 1-4 of the 
breadth. 
Small streams of the Knobs, rare, one or 
two inches: tooth obtuse, projection very 
small. 
110 S p. Alasm. papyraceum (Sulcularia pa- 
pyraceadisc. 1821.) Shell very thin and flat, 
elliptical, broader behind, truncate crenate 
with furrows and broad ribs: outside oliva- 
ceous a little uneven, inside bluish. Length 
one half, diameter 2-9, axis one fourth of 
breadth. 
In East Kentucky. Very rare ; 2 or 3 
inches, tooth short and wide, projection with 
an oblique fold; the posterior ribs are seers 
both outside and inside. 
Ill Genus or tribe Lasmonos. 
S N. G. Lasmonos. Cardinal tooth 
none, remplaced by a sinus, a flat tubercle, 
and a decurrent enamel. Lamellar tooth 
curved following the beak. General form of 
Metaptera with a small coalescent wing. 
Ill Sp. Lasmonos Fragilis. disc. 1822.— 
Shell very thin, depressed, suboval, broader 
behind, with a small wing, some nodulotities 
behind, outside smooth olivaceous, inside? 
