ORDOVICIAN FAUNAS. 177 
groove, which slopes down to the angular or sharply-rounded side of 
the volution. While the central pair of ridges increases in prominence, 
the lateral pair becomes more and more indistinct on the last volution, 
till, at the apertural margin, they are scarcely distinguishable—at any 
rate, this is true of casts. The transverse surface markings are promi- 
nent, regular, visible to the unassisted eye, about three in 1 mm.; the 
course of the stris from the umbilicus is at first nearly straight across, 
and it is only in the centro-lateral grooves that they curve backward 
very strongly. When the characters of the external layer are pre- 
served, these very fine, short lines are to be seen crossing the trans- 
verse lines rectangularly.”—UlIrich and Scofield. 
BUCANIA PUNCTIFRONS (Hmm.). 
Plate XII., Figs. 10-12. 
1842. Bellerophon punctifrons Emm., Geol. Rep. 2d Dist. N. Y., p. 
392, fig. 5. 
1847. Bucania punctifrons Hall, Pal. N. Y., vol. I., p. 18%, pl. 40 A, 
figs. 1 a-e. 
1897. Bucama punctifrons U. & S., Pal. Minn., pt. II., p. 894, pl. 
67, figs. 41-44. 
Description—‘‘Shel] rather small, probably not exceeding 20 mm. 
in height. Volutions three or four and a half, rounded on the back, 
subangular on the sides; umbilicus large, its width somewhat greater 
than half the height of the shell; aperture slightly wider than high, 
subpentagonal. In a transverse section the volutions are semi-circular 
in the dorsal half, with the umbilical slopes almost straight and the 
ventral side broadly indented by the preceding whorl. The width 
of the last volution expands from 6 mm. to 12 mm. in a specimen 18 
mm. high. In the same specimen the slit has a length of 16.5 mm. 
and a width of 0.7 mm. The slit-band is concave, bordered on each 
side by a delicate line and crossed by numerous fine lunule. On each 
side of the slit and band the whole exposed surface is covered by a 
strong and very sharply-defined network, the deep meshes of which 
are so arranged that they form rows running in two directions, one 
12 
