BRYOZOA. 199 
Arthroclema 
placed near the upper end. Zocecia in five or six longitudinal rows, with small 
oblique apertures, the posterior margin prominent; arranged in transverse rows, 
with six the usual number in the length of the segment; short segments (2.5 mm.) 
have five. Surface distinctly striated lengthwise, often thrown into strong, but 
never sharp, ridges between which the zoccial apertures are arranged, The latter 
are always difficult to see. In drawing fig. 30 I overlooked them entirely, having 
mistaken certain depressions, which are often met with in these segments, for them. 
Since freeing the specimen from the matrix I find that it has really five rows of 
apertures, both longitudinally and transversely, of the same size as shown in fig. 33. 
With this correction the figure may still be of aid in the identification of the species, 
because it shows the striation of the surface better than the original of fig. 28. It 
should be added, however, that the latter shows the usual shape of the segments 
better. | 
Secondary segments five-sided, 2.7 to 3.2 mm. long, the length depending upon 
- the number (six or seven) of transverse rows of zocecial apertures, 0.35 to 0.5 mm, in 
diameter, the ends usually a little wider, the upper flat, the lower rounded. Zocecial 
apertures in five longitudinal and six or seven transverse rows, small, oblique, drawn 
out above, their ends widely separated. Interspaces finely striated lengthwise, the 
angles sharp or rounded, formed by a raised central line and one or two similar lines 
on each side of it. An articulating scar or shallow socket has been observed just 
above one of the first cycle of zocecial apertures, but their presence in the segments 
of this set is to be counted as an unusual occurrence. For this reason it is more 
than probable that most of the segments which are next described as tertiary are 
really young or terminal joints of the second order. 
Tertiary segments about 3.0 mm. long, less than 0.35 mm. in diameter, very 
slender, four or five-sided, with sharp angles, the lower end rounded and tapering 
slightly, the upper sharply truncate. Zocecia in four or five longitudinal rows, in 
six, but oftener in seven cycles, their apertures small, oblique, the raised margin 
highest posteriorly and running out on each side to the angle ridges. Behind each 
aperture usually a pair of very delicate striz, the conditions being very much as in 
Helopora spiniformis (see plate III, fig. 4). Angles formed by a single raised line. 
These segments are distinguished from those of the second order by their greater 
tenuity, more oblique zocecial apertures, and absence of strive on the sides of the 
angle ridges. 
As stated in the paragraph preceding the last, it is possible that many of the 
segments just described as of the tertiary set really represent the young stage of the 
secondary set. In that case it is probable that the four-sided joints only are ter- 
tiaries. 
