CONCHOLOGICAL WRITINGS. 19 
3. DecuRAMBIS. Cardinal tooth bilobe flexuose enamelled, de- 
current on both sides, decurrence on remplacing the aenalld tooth 
behind, no angular knob to it. 
4. SuncunariA. Cardinal tooth small striated decurrent before, 
separated by an oblique furrow from a small oblique projection 
remplacing the lamellar tooth, with a small fold in it. 
All these shells are transversal and inequilateral; 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 ribbed 
behind: yellowish and laminated outside, white and uneven inside. 
Length 3-5, diameter 1-3, axis 1-3 of the breadth. 
In lower Ohio and in the Mississippii—Large heavy shell, five to 
six inches broad, roughly rugose outside by their concentric lamina. 
Cardinal tooth nearly trilobe, lamellar angle obtuse, confluent 
together. 
If these characters of the teeth should separate it from the Las- 
migona, it may be called Gonamblus. 
103 Sp. Alasmodon rugosum' (ZL. 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, 6 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 incarnate. 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 projection acute 
‘before, obtuse behind. Beak or apex a little prominent and slightly 
rugose. Very rare. 
