462 
THE PALEONTOLOGY OF MINNESOTA. 
[Rhynchotrenia capax 
Rhynchotrema capax Conrad, sp. 
PLATE XXXIV. FIGS. 30-34. 
1842. Atrypa capax Conrad. Journal of the Academy of Natural Sciences of Philadelphia. 
vol. viii, p. 264, pi. xiv, fig. 21. 
1847. Atrypa increbescens (partim) Hall. Palaeontology of New York, vol. i, p. 146, pi. xxxiii, 
figs. 13i, 13k-13y. 
1856. Atrypa increbescens (partim) Billlngs. Candian Naturalist and Geologist, vol. i, p. 207, 
flgs. 15, 16. 
1860. Atrypa increbescens Hall (not 1847). Thirteenth Report, New York State Cabinet of Natural 
History, p. 66, flgs. 6, 7, 9-11. 
1862. Rhynchonella increbescens (partim) Hall. Geology of Wisconsin, vol. i, p. 55, flgs. 5-7. 
1863. Rhynchonella capax Bfllixgs. Geology of Canada, p. 211, fig. 213. 
1873. Rhynchonella capax Meek. Paleontology of Ohio, vol. i, p. 123, pi. xi, fig. 2. 
1875. Rhynchonella capax Miller. Cincinnati Quarterly Journal of Science, vol. ii, p. 17. 
1880. Rhynchonella capax White. Second Annual Report, Indiana Bureau of Statistics and 
Geology, p. 489, pi. i, flgs. 9-11. 
18S1. Rhynchonella capax White. Tenth Report of the State Geologist of Indiana, p. 121, pi. i, 
flgs. 9-11. 
1882. Rhynchonella capax Whitfield. Geology of Wisconsin, vol. iv, p. 263, pi. xn, flgs. 26, 27. 
Description: "Shell attaining about a medium size, varying with age from com- 
pressed subtrigonal to subglobose, old examples being often more convex than their 
diameter in any other direction; posterior lateral margins somewhat straightened 
and converging to the beaks at about a right angle in young shells, but becoming 
more rounded in the adult; lateral margins rounding to the front, which is more or 
less distinctly sinuous, or nearly straight in the middle. 
" Dorsal valve generally a little more convex than the other, most prominent in 
the middle and rounding abruptly or sloping more gently from the central region in 
all directions; the more elevated part forming anteriorly a depressed mesial ridge 
that is nearly flat and occupied by four plications on top, and rarely continues two- 
thirds of the way to the strongly incurved beak, while on young or compressed indi- 
viduals it is faintly marked even anteriorly; lateral slopes each occupied by four to 
seven or eight simple angular plications." Interior with the apex much thickened 
and converging anteriorly into a prominent subaugular median septum, which 
extends about half way to the front margin; bases of the crural processes prominent 
and drawn out into slender inwardly and upwardly curving hooks, between which 
there is a thin, but often strongly elevated, cardinal process, while on the outside of 
the former are the large dental cavities; on each side of the septum in the posterior 
half are two pairs of deeply excavated adductor scars, the anterior pair being the 
larger. 
" Ventral valve with its beak abruptly pointed and very strongly incurved upon 
that of the other valve in adult shells, but less distinctly curved and showing a small 
