434 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Our species agrees with M. goldfussi in the greater posterior pro- 
longation of the shell, and the rounded anterior portion which does 
not advance much beyond the beak; the numerous concentric growth 
lines give it a roughened appearance. It differs from the figures 
given of that species in the stronger and broader posterior radial 
ridge, with two instead of one radial rib in the sinus, and in the ab- 
sence of prominent radial ribs from the flattened area, posterior to 
the radial ridge, where M. goldfussi has about three strong radial ribs. 
The figures ^ of M. goldfussi show from 14 to 16 ribs, much narrower 
than their interspaces, and apparently continuous to the anterior 
edge of the shell, while our species bears from 17 to 19 ribs which are 
wider than the interspaces and do not continue to the anterior edge 
of the shell, representing thus a less primitive form for the latter 
species. Our species differs also in having three or four strong Tri- 
gonia-like ridges extending transversely across the umbo. These 
growth ridges die out upon all portions of the shell except the extreme 
anterior area where they may be traced almost half-way down the 
shell. 
M. goldfussi is characteristic of the Upper Trias (uppermost Mus- 
chelkalk through Rhaetic) of the Alps and Carpathians. 
It is interesting to note the apparent close relationship between 
Trigonia and Myophoria, for the Sutton specimens have the shape 
and radial markings of Myophoria and at the umbo have the strong, 
transverse ridges similar to Trigonia; added to this, the continuance 
of the radial ribs to the beak suggests the derivation of both from the 
same ancestor rather than the descent of one from the other. 
Choristoceras suttonensis n. sp. 
PI. 40, figs. 4, 6. 
Whorls laterally compressed, but little or not at all embracing as 
evidenced by the absence of any impressed zone, and increasing very 
slowly in size. Cross-section oval with breadth al)out four fifths of 
the height; sides broadly rounded; venter shghtly flattened. 
Surface ornamented with strong simple ribs that cross the umbilical 
region, though there much weaker, increase in strength u'p the sides 
1 A. Bittner. Lamellibranchiaton der alpinen Trias. Alihandl. k. k. geol. Reichs- 
anstalt, Wlen, 1895, vol. 18, pt. 1, pi. 11, fig. 24-27. 
