BRYOZOA. 241 
Homotrypa tuberculata.] 
Zoarium small, ramose, branches rounded or flattened, dividing rather fre- 
quently, 2.0 to 3.5 mm. thick, and 2.5 to 7.0 mm. wide. Surface more or less 
strongly tuberculated, the monticules 2 to 2.5 mm. apart, conical, often very prom- 
inent. Zocecial apertures nearly fourteen. in 5 mm., angular or rounded, more or 
less oblique except in the oldest examples, in most specimens exposing the cysti- 
phragms. Walls thin, often separating so as to form considerable interspaces in 
which a greater or less number of closed mesopores is contained. The extent of 
these interspaces varies greatly, being sufficient in some instances to cause the 
zocecial apertures to be of rounded or ovate form, while in other specimens they are 
scarcely appreciable. Acanthopores small, about one to each zocecium. 
Internal characters: In vertical sections the tubes are large and without dia- 
phragms in the axial region, the latter, together with short and rather irregular 
series of cystiphragms, being developed in the narrow peripheral region only. 
The mesopores appear as shown in the figure. Of tangential sections it would be pos- 
sible to select small portions differing so much from each other in the number of 
mesopores that they would scarcely be suspected of belonging to one species. Still, 
if the sections are large enough each will contain some parts that may be said to be 
practically the same as those represented in figs. c andd. The acanthopores, though 
small and few, are quite distinct in these sections. 
This is another of those aberrant forms of the genus like H. intercalaris. While 
its relations seem often to be decidedly suggestive of Homotrypella (2?) ovata, I do not 
believe that its development resulted in that form. It seems to be an offshoot, per- 
haps from that line, which latter produced the H. obliqua Ulrich, of the Cincinnati 
group. 
The strong monticules distinguish the species from the Trenton forms of the 
genus. Associated with it there are two really very distinct though dangerously 
similar species. The first of these is the Atactoporella ramosa with its numerous 
acanthopores and inflected zocecial apertures, and totally different internal struc- 
ture. The second, Callopora persimilis, differs so widely in its internal structure 
that it will be sufficient to refer the student to the figures on plate XXII. Other 
species presenting more or less superficial resemblance might be mentioned, but I 
cannot regard it as necessary, since with the aid of thin sections the student will 
have no trouble in distinguishing them. 
Formation and locality.—Upper third of the Trenton shales, near Cannon Falls, Minnesota. The 
species probably occurs in the same beds at St. Paul. 
Mus. Reg. No. 8123. 
