SILURIAN FAUNAS. 
9 
cave) 
(os) 
ZAPHRENTIS sp. undet. 
Plate XVII., Figs. 9-10. 
Numerous specimens of horn coral, usually imperfectly preserved, 
are present in the fauna of the coralline bed at the summit of the 
Decker Ferry formation. Several species are probably present, but 
all are too imperfectly represented for satisfactory study. Other 
specimens representing the same genus are more rarely present in the 
lower strata of the formation. | 
HY DROZOA. 
Seeoaeon CONCENTRICA Goldf. 
Masses of a stromatoporoid hydrozoon are not uncommon in the 
coralline layer at the summit of the Decker Ferry formation, which 
may be provisionally referred to Stromatopora concentrica. In none 
of the specimens examined in thin section were the characters suffi- 
ciently well preserved for accurate identification. 
MOLLUSCOIDEA. 
BRYOZOA. 
MONOTRYPA CORRUGATA DN. Sp. 
Plate XVIII., Figs. 1-5. 
Deservption.—Zoarium forming lenticular or hemispheric masses. 
A large hemispheric specimen has a diameter of 40 mm., with a height 
of 22 mm., the base being concavely excavated to a depth of 7 mm. 
Other specimens are frequently much flatter, sometimes with a height 
of not more than 5 mm. The celluliferous surface of the zoarium is 
usually so closely covered with matrix that the zeecial apertures are 
not exhibited. In longitudinal fractures the zoccial walls separate 
readily along their median lines, and the walls themselves are seen 
