XXXVlll 
INTRODUCTION. 
with long tubular zooecia, of which the apertures are separated 
by a thickening of the wall of the zoarium. 
Fig. 8. — Callopora elegantula, Hall. 
Silurian — Niagara Group : Lock- 
port, N.Y. Tangential section ; 
X 18. (After Ulrich.) 
Fig. 9. — Heterotrypa injlecta^ Ulrich. 
Ordovician— Cincinnati Group : Cin- 
cinnati, 0. Vertical section ; x 12. 
(Reduced from Ulrich.) 
Pig. 8, of Callopora^ with its abundant diaphragms and narrow 
mesopores, has essentially the same structure as some Jurassic 
species (cf. Heteropora conifera^ B.M. Cat. Jur. Bry. p. 205, fig. 19«); 
Heterotrypa (Fig. 9), with its rare diapiiragms and moniliform 
walls, agrees with the structures of Ceriopora farringdonensis, 
Greg., and Ceriopora ttiherosa (Horn.), shown in Figs. 42 and 45 of 
Fig. 10. — Atactoporella ortoni, Nicholson. Ordovician — Cincinnati Group : 
Cincinnati, 0. Vertical section of a specimen consisting of two layers of 
cells ; X 35. (After Ulrich.) 
this volume; while Atactoporella (Fig. 10) resembles in its multi- 
lamellar zoarium the structure of Multicrescis laminata (Greg.), 
B.M. Cat. Jur. Bry. pi. xi. fig. 3i, or the Multicrescis tuherosa 
(Edm.) of Fig. 54 of this volume. 
