BRYOZOA. 187 
Arthrostylus. ] 
sidered tubular in the sense attaching to that term when applied to the Cyclostomata. 
On the contrary they are no more so than are the zovecia of the most typical Rhinidic- 
tyonide. In tangential sections they are oblong-quadrate or hexagonal in outline. 
Hemisepta have not been observed, but rows of minute tubuli occur between the 
walls of adjoining zocecia and sometimes in the longitudinal interspaces in the ves- 
tibular region. A minute tube is also to be detected running from end to end through 
the axis of the segments. 
Respecting the position of the family the jointed character of the zoaria leads 
us to look for its relationship first with the similarly constructed Cellariide. The 
latter embraces living forms chiefly, and of many of these I have secured specimens, 
so that I am now in a position to speak intelligently upon their characters, as com- 
pared with paleozoic forms. I would be glad to do this here were it not that I would 
thereby interfere with my plans for a general work on inter-relation of bryozoan 
types. It will probably be sufficient to say that the two families are distinguishable, 
and that the relationship between them, if any exists, is almost certainly less inti- 
mate than that between the Arthrostylidw and Rhinidictyonide. 
Aside from the wedge-shaped form of the primitive cells in the Arthrostylide, 
which it is evident resulted necessarily from their radial arrangement about a linear 
central axis, they are precisely like those of true Rhinidictya. They agree also in 
possessing median tubuli between the walls of adjoining zocecia. Then again I am 
convinced that the minute axial tube of the Arthrestylide is functionally identical 
with the median tubuli between the mesial lamine that are such a characteristic 
mark of the Rhinidictyonide. The jointed character of the zoarium even, is not 
unknown in the latter since it pertains to Dicranopora, Ulrich, a genus that in all 
other respects is precisely like Rhinidictya. Really, I find only one structural differ- 
ence between the two families, and that is that while the zocecia in the Rhinidicty- 
onde are arranged so as to form bifoliate zoaria—in other words, are disposed in 
two equal expansions grown together back to back, they are arranged radially 
around a central axis, forming subcylindrical zoaria, in the Arthrostylide. 
Genus ARTHROSTYLUS, Ulrich. 
Arthronema, ULRICH, 1882. Jour. Cin. Soc. Nat. Hist., vol. v, pp. 157 and 160 (not EscHSCHOLTz, 
who used the name for a genus of Colpodea). 
Arthrostylus, ULRICH, 1888. Amer. Geologist, vol. i, p. 230; 1890, Jour. Cin. Soc. Nat. Hist., vol, xii, 
p. 188; 1890, Ill. Geol. Sur., vol. viii, p. 400. 
Zoaria bushy, branching dichotomously, the whole consisting of numerous, 
exceedingly slender, subquadrate, equal segments, joined to each other by terminal 
articulation, Zocecia arranged in three (perhaps more) rows, usually between 
