BRYOZOA. 103 
Introduction.] 
7. The frondescent or palmate zoarium is a modification of the ramose, differing 
from it in the flattening and expansion of the branches. Examples are Heterotrypa 
frondosa VOrbigny and Homotrypa flabellata Ulrich. 
8. The jointed zoarium, in which it is divisible into a greater or less number of 
subequal segments. that articulate with each other either terminally or by means of 
lateral sockets ; is illustrated in Helopora, Arthroclema and Arthropora. 
9. The fenestrated ov inosculating zoarium, as in Fenestella and Phylloporina. 
The pinnate zoarium is a modification in which the parts of the fronds are feather- 
like in their arrangement. Pinnatopora and Acanthocladia are examples. 
If the specimens under investigation fall under any except the last two modes 
of growth, they will probably exhibit either groups of cell-apertures larger than the 
average, commonly raised above the surface and therefore known as “ monticules ”; 
or clusters of small cells or smooth spots called ‘“macule.’’ The monticules may be 
rounded, low or conical, and sometimes ridge-like. Examples are shown on plate 
XXII, in figs. 1, 18 and 24. Frequently there is a combination of large and small cells 
as in figs. 18 and 19 of the same plate. True macule are best developed in the 
Fistuliporide, in which they consist of aggregations of lenticular vesicles, but on 
plate XVI, fig. 6, is a good example of the kind in which the cells are tubular. The 
non-poriferous margins, so common among the bifoliate Bryozoa, are most probably 
a modification of the maculz ; see plate VIII, fig. 19. 
The presence or absence of interstitial cells between the ordinary zocecia, and 
the determination of their character when present, is the third step in our investi- 
gation. These cells may be of the nature of ‘“mesopores”—small, closely-tabulated 
tubes, as in Prasopora and Callopora (plates XVI, XXI, and XXII), or the interspaces 
may be occupied by “vesicular tissue” as shown in fig. 4 on plate 1X, a vertical 
section of Pachydictya frondosa. The zoarium of Monotrypa is characterized by the 
complete absence of both mesopores and vesicles (see plate XX VI, figs. 24-29). 
Important diagnostic characters are to be observed in the character of the 
mouths of the zocecia. They may form short tubular projections (plate I, fig. 6), be 
enclosed by a smooth rim or peristome (plate I, figs. 17 and 28), or the rim may be 
minutely papillose (plate XIV, fig. 22); or the mouth may be depressed and situated 
in a sloping area (plate X, fig. 24). Other conditions, described by the terms “ direct,” 
“oblique,” and “confluent,” are obvious without the citation of examples. 
Of other external features, the arrangement of the zoccial’ apertures, and the 
character and marking of the interspaces should be noticed. 
In the further progress of the investigation, which is now carried on chiefly by 
means of thin sections, it is necessary to determine the presence or absence, and the 
