90 
Kirtley F. Mather 
1903. Zaphrentis gibsoni. Girty, Prof. Paper, U. S. Geol. Surv., No. 16, 
p. 323. 
Middle and upper portion of Hermosa formation: San Juan 
region, Colorado. 
Weber limestone: Crested Butte district, Colorado. 
This species is represented by about a dozen specimens in 
none of which has the calyx been well preserved. Sections at 
several different stages of growth indicate the arrangement of 
septa which is characteristic of Zaphrentis as that genus is 
ordinarily interpreted. The major septa are divided into four 
quadrants by the conspicuous cardinal fossula bisected by the 
cardinal septum, the less conspicuous alar fossulae, and the 
scarcely perceptible counter fossula. There is a tendency for 
the major septa to fuse together at their inner ends. Exter- 
nally the corals appear to resemble so closely the published figures 
and descriptions of Zaphrentis gibsoni that they are referred to 
that species with considerable confidence. 
Horizon and locality. Brentwood limestone : near Fayetteville, 
Arkansas (Stations 134, 135, and 152) ; Sawney Hollow, Okla- 
homa (Station 210). ?Kessler limestone: East Mountain, 
Fayetteville, Arkansas (?Station 209). Morrow formation: 
near Ft. Gibson, Oklahoma (Station 296). 
Genus AMPLEXUS Sowerby 
Amplexus corrugatus n. sp. 
Plate /, figures 7-10. 
Description. Corallum slender, conical in the lower portion 
and cylindrical in the mature stages of its growth, constricted 
at irregular intervals, many individuals geniculated, ordinarily 
gently curved, rarely straight, attaining a diameter of 6 or 7 mm. 
before a length of 20 mm. is reached, thereafter varying in 
diameter between 5 and 9 mm. ; epitheca thin, longitudinally 
ribbed and concentrically striated, the striae more conspicuous 
immediately preceding the constrictions than elsewhere, bearing 
a few erect, hollow, tubular spines irregularly scattered over its 
surface but more numerous on the youthful conical portion of 
the corallum than on the mature cylindrical part ; calyx not well 
displayed in any of the specimens at hand but probably deep. 
In transverse sections the septa are seen to be about 22 or 
24 in number in the mature regions and to extend slightly over 
