FRESH WATER AND LAND SHELLS. 49 
by D’Orbigny. It is very peculiar in the texture of the epidermis, which is crimpled up 
into irregular, somewhat parallel, very close, rugose lines, which cover the whole surface 
of the disk. In both of these valves there is a distinct muscular impression above the 
great anterior cicatrix, which I have not observed before in any of the Anodontz. The 
absence of a dorsal cicatrix is also unusual; but in this it resembles some of the other 
South American species, viz.: Anodonta ensiformis, Spix, soleniformis, D’Orb, &c. In 
outline it is nearly allied to An. exilis, (Nobis,) but it has not the straight dorsal line, 
is a thicker shell, and has a very different epidermis. The triangular fosset at the end 
of the ligament is rather large and well marked. The right valve has a few black pen- 
cilled marks in the nacre, such as are sometimes seen in the South American Anodontz. 
These are remarkable as being nearly parallel, and in a direction pointing to the beaks. 
They look as if made by a pen, with black ink. 
I name this fine species in honour of the memory of Schroster, author of Flusconchlien, 
&e. 
Anoponta Arxkansensis. Pl. XXIX. Fig. 56. 
Testa levi, ellipticd, compressa, valdé inxquilaterali, posticée subbiangulata; valvulis crassis; natibus 
subprominentibus, ad apices undulatis; epidermide subviridi, radiata, striatds; margarita cxruleo-alba. 
Shell smooth, elliptical, compressed, very inequilateral, subbiangular behind; valves thick; beaks rather 
prominent and undulated at the tip; epidermis greenish, rayed; nacre bluish-white. 
Hab. Little Arkansas, J. L. Le Conte, M. D. 
Cabinet of Major Le Conte. 
Diam. .9, Length 1.7, Breadth 3 inches. 
Shell smooth, elliptical, compressed, subbiangular behind and rounded before, sub- 
angular on the posterior slope; substance of the shell thick; beaks rather prominent, 
pointed, with three or four large undulations at the tip; ligament long and rather thin; 
epidermis greenish, striate, with unequal transverse marks of growth, dark on the pos- 
terior slope, with indistinct, broad greenish rays over the disk; posterior slope with two 
lines from the beak to the posterior margin; dorsal margin slightly curved, and having a 
callus immediately under the beak almost amounting to a tooth; anterior cicatrices dis- 
tinct; posterior cicatrices confluent; dorsal cicatrices placed on the lower part of the 
callus; cavity of the shell rather shallow; cavity of the beaks shallow and angular; nacre 
bluish-white, leaving a broad dark margin. 
Remarks.—A single specimen of this interesting species has been submitted to me by 
Dr. J. L. Le Conte, who obtained it on a late scientific excursion to the Rocky Moun- 
tains, from the Little Arkansas, where the road to Santa Fé crosses it. This species is 
not likely to be confounded with any other known to me, and belongs to that group which 
has an irregular thickening or callus under the beak on the dorsal margin, which, while 
it does not amount to a tooth, makes a very distinct natural group, This callus is not 
so large and marked as to be confounded with D’Orbigny’s genus Monocondylea; but it 
may be compared with that of Alasmodonta edentula, Say, which is a true Anodonta. ‘The 
form of this species is more lenticular than in any other of the genus I know; and look- 
i, 
