Revision of Bryozoan Genera.—Cumings. 205 
Acanthopores are numerous and conspicuously of two sizes, as is 
best shown in fig. 7, Pl. X, (x 43). They are not confined to the 
angles of the zocecia, but frequently indent their walls. 
Longitudinal sections (fig. 3, Pl. X) show that the mature region 
is very deep, the thickness of the zoccial walls varying but little from 
where the tubes bend outward, to the surface. The large acanthopores 
are conspicuous features of such sections. (a, fig. 3, Pl. X.) The 
walls present the beaded appearance characteristic of the genus. This 
I believe is in some cases due to the fact that the section cuts in and 
out of the side of an acanthopore. The large acanthopores traverse the 
entire mature region and are sometimes present even in the axial re- 
gion. Diaphragms are abundantly developed, horizontal or, rarely, 
curved, or infundibular, from one-third to two tube-diameters apart 
in the zocecia, and closer set in the mesopores. The walls of the 
latter are constricted where the diaphragms join them. 
In the crowded diaphragms, beaded walls, constricted meso- 
pores, and two sizes of acanthopores, this species is a typical 
Dekayella, very similar to D. ulrichi-robusta (pl. X., fig. 2, 
pl. IX, fig. 4). In the thinness of the walls and fewness of the 
mesopores it is a typical Dekayia (cf. figs. 7 and 10, pl. IX; 
figs. 7 and 10, pl. X), and may be compared with such a form 
as D. Multispinosa Ulr.* In the shape of the zoarium, fre- 
quency and expression of the monticules and tabulation of the 
zocecia Dekayia subfrondosa is very similar to D. perfrondosa 
(vy. fig. 1, pl. XI; fig. 1, pl. X).7 
The tangential sections of the type species Dekayia aspera 
E. & H. inserted for comparison (fig. 10, pl. IX; fig 10, pl. X) 
have the acanthopores just as certainly of two sizes as in any 
Dekayella. This is well shown in fig. 10, pl. X, (x43) in 
which the ratio of size of the largest and smallest acantho- 
pores seen is about as five to one. The ratio in a similar sec- 
tion of Dekayella ulrichi-robusta is as seven to two (see pl. 
X, fig. 9). 
In this case, therefore, the size of the acanthopores, thick- 
ness of the walls, tabulation of the zocecia and type of growth 
all fail to serve us in attempting to refer the form to one of the 
three genera Dekayia, Dekayella and Heterotrypa (as restrict- 
ed by Ulrich). 
The size of the acanthopores is perhaps of most interest, 
as it is on this character mainly that Mr. Ulrich’s genera are 
* Jour. Cin. Soc. Nat. Hist., vol. vi, 1883, pl. 6, fig 8. 
+ Cf. also H affinis. geol. Ill, viii, pl. 36, fig. 2a, and Leptotrypa stidhami, 
Ibid., pl. 36, fig. 4 a. . rs “a 
