212 The American Geologist. April, 1902. 
a single genus, to which the prior term Dekayia should be ap- 
plied. The following is a diagnosis of this genus as amended: 
Zoarium ramose, or variously compressed, or lobed, or frondescent; 
growing upward from a more or less broadly expanded basal attach- 
ment. Surface smooth or variously ornamented with monticules, ma- 
cule or spines. The cells in the monticules and macule may be either 
larger or smaller than the average. 
Zocecia polygonal, subpolygonal or rounded. Mesopores few to 
numerous, angular. Acanthopores always present, typically of two 
sizes, the smaller present only in. the mature region. 
Interzocecial walls always thin in the axial region and sometimes 
in the mature region; at times considerably thickened in the mature 
region, always consisting (in sections of the mature region) of three 
elements: a median zone (usually light-colored) in which are lodged 
the mesopores and acanthopores, a definite dark band on either side 
bounding the median zone and encircling the zocecia, and a band (us- 
ually light-colored) of schlerenchyma immediately encircling the zo- 
cecial cavity. 
Diaphragms few or almost lacking, to numerous; nearly always 
straight and horizontal. Only in exceptional cases are cystoid dia- 
phragms present. Ordovician. 
The wall structure (see Pl. X, figs, 10 and 4) is, I believe, the 
most stable character of the genus. 
Dekayia as thus defined will include the following species 
and varieties: Heterotrypa frondosa Ulr. (=D. perfrondosa), 
H. affinis Ulr., H. paupera (Ulr.)N.& B., H. singularis Ulr., 
H. inflecta Ulr., (=D. ulrichi-inflecta), H. solitaria Ulr., H. 
subpulchella Nich. ( = D. perfrondosa-subpulchella), H. proli- 
fica Ulr. (=D. perfrondosa-prolifica), H. subramosa (Ulr.) 
N. & B.; Dekayia aspera E. & H., D. appressa Ulr., D. macula- 
ta James, D. multispinosa Ulr., D. pelliculata Ulr., Dekayella 
ulrichi (Nich.) Ulr., Dekayia ulrichi-expansa Cumings, D. ul- 
richi-lobata Cumings, Dekayella ulrichi-robusta Foord, D. ob- 
scura Ulr., (=Dekayia ulrichi-obscura), Dekayella praenuntia 
Ulr., D. praenuntia-echinata Ulr., D. praenuntia-multipora Ulr., 
D. praenuntia-naevigera Ulr., D. praenuntia-simplex Ulr., D. 
trentonensis (Ulr.) N. & B., D. perfrondosa-cystata Cumings. 
Dekayia magna Cumings probably represents the basal part 
of D. aspera (E. & H.): heterotrypa barrandei, H. monilifor- 
mis and Dekayia devonica probably do not belong in this group. 
General Observations—tThe relationships suggested by a 
careful study of numerous specimens of some of the above 
forms are so striking that I am convinced that we are dealing 
