214 The American Geologist. April, 195%. 
true connecting link between D. perfrondosa and D. ulrichi- 
robusta. 
The intermediate character of Dekayia subfrondosa has al- 
ready been pointed out. It occurs associated with D. ulrichi- 
robusta and the lowest specimens of D. perfrondosa, and is 
connected with the latter by such 1orms as shown in figs. 9, 
11, 12 and 13, pl. 1X, while parts of tangential sections in which 
mesopores are abundant remind one very strongly of the for- 
mer. Fig. 11 is from a specimen in which the diaphragms are 
crowded and the mature region deep, very much as in D. sub- 
frondosa. The appearance of the interzocecial walls, mesopores 
and acanthopores is quite similar to fig. 15, a typical perfron- 
dosa. Sections cutting the submature region of D. perfrondo- 
sa present the same appearance as sections of the mature re- 
gion of D. subfrondosa (cf. figs. 8 and 9, pl. IX; figs 6 and 7 
pl. X), showing that the only difference between the two is 
the thickening of the walls and development of mesopores in 
the adult stage of D. perfrondosa.* 
In Dekayia aspera as shown in fig. 10, pl. IX, and fig. 10, pl. 
X, the walls in the mature region are slightly thicker than in 
D, subfrondosa (thinner than in D. perfrondosa), and the large 
set of acanthopores is extravagantly developed. The small 
acanthopores are of the normal size for Heterotrypa Ulr. That 
the large acanthopores are sometimes suppressed in D. aspera, 
at least in portions of the zoarium, seems practically certain.+ 
The main difference between it and such forms as D. Sub- 
frondosa and D. perfrondosa is in the almost total absence of 
diaphragms in D. aspera (and a few closely allied forms). Yet 
in D, perfrondosa these structures may be comparatively few 
in the zocecia,t though never entirely lacking as is occasionally 
the case in D. aspera. 
Finally Mr. Ulrich has himself long ago pointed out the 
extreme tenuity of the line between Dekayia and Heterotrypa 
Ulr., because of such connecting forms as D paupera§ and an 
*Compare the thickening of the walls, amounting in some cases to the com- 
plete filling up of the zooecia in senile stages of some recent Bryozoa. 
+Dakayia magna Cumings, is such aform,.. Many sections were prepared 
ofthis form without detecting acanthopores of more than ordinary size; yet I 
am now fully convinced that it is a true D. aspera, probably from its large size 
and cylindrical form, the basal portion of a colony. 
tIn tact Nicholson says of this species that the tabula are “comparatively 
few and remote" in the “large corallites.’’ Genus Monticulipora, p. 105. 
§Jour, Cin. Soc, Nat. Hist. vol. vi, 1883, p. 85. 
