462 THE PALEONTOLOGY OF MINNESOTA. 



[Bhynohotreraa <-;i|i:i \ 



RHYNCHOTREMA CAPAX Conrad, sp. 



PLATE XXXIV, FIGS. aO-;t4. 



1842. Atrypa capax CONRAD. Journal of the Academy of Natural Sciences of Philadelphia, 



vol. viii, p. 264, pi. xiv, flg. 21. 

 1847. Atrypa inerebescens (parfcim) HALL. Paleontology of New York, vol. i, p. 146, pi. xxxirt, 



flgs. 13i, 13k-13y. 

 1856. Atrypa inerebescens (partim) BILLINGS. Candian Naturalist and Geologist, vol. i, p. 207, 



flgs. 15, 16. 

 1860. Atrypa inerebescens HALL (not 1847). Thirteenth Report, New York State Cabinet of Natural 



History, p. 66, flgs. 6, 7, 9-11. 



1862. Rhynchonella inerebescens (partim) HALL. Geology of Wisconsin, vol. i, p. 55, flgs. 5-7. 



1863. Rhynchonella capax BILLINGS. Geology of Canada, p. 211, flg. 213. 



1873. Rhynchonella capax MEEK. Palaeontology of Ohio, vol. i. p. 123, pi. xi, flg. 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. 



1881. 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 



