BRYOZOA. 299 
Hemiphragma.] 
Genus HEMIPHRAGMA, n. gen. 
Batostoma (part.) ULRICH, 1890. Geol. Surv. Ill, vol. viii, p. 379. 
Zoaria like those of Batostoma save in this, that the diaphragms in the periph- 
eral part of the zoccial tubes are incomplete. 
Type: Batostoma irrasum Ulrich. 
The discovery of a fourth species having incomplete diaphragms has decided 
me in giving the character generic rank. What may prove to be a fifth species, 
occurs among my material from the upper beds of the Hudson river group at 
Delafield and Iron Ridge, Wisconsin. Unfortunately, the Bryozoa which occur so 
abundantly at those localities do not preserve the internal characters, so that in 
cases like this it is impossible to verify the generic affinities of the species by means 
of thin sections. It is possible that the natural relations of Hemiphragma are not 
with Batostoma, but in the absence of data showing the value of the difference be- 
tween the two genera, we are obliged to place them together because of their 
marked agreement in all other respects. 
HeMIPHRAGMA IRRASUM Ulrich. 
PLATE XXIV, FIGS. 5-19, 
Batostoma irrasa ULRICH, 1886. Fourteenth Ann. Rept. Geo. Nat. Hist. Sur. Minn., p. 94. 
Zoarium consisting of small, subcylindrical, frequently and rather irregularly 
dividing branches, commonly 5 or 6 mm. in diameter, but varying from 4 to 8 mm., 
the latter extreme probably only when an extra layer of tubes has grown over the 
original branch. Monticules wanting, but under fully matured conditions the sur- 
face is abundantly spinulose. Zocecia with subangular apertures and thin walls 
when young, and with smaller, subcircular or oval apertures and more or less thick 
walls in fully matured examples; arrangement of apertures rather regular in rows 
about small solid spots, in the immediate vicinity of which the zocecia may be of 
larger size than elsewhere; seven to nine in 3mm. Interspaces apparently solid 
and generally with shallow irregular depressions in most specimens, but in very 
young stages a variable number of irregular mesopores may be recognized. Acan- 
thopores numerous, two or more to each zocecium, situated in the angles of junction 
and interspaces, and increasing in size with age. They are large and a conspicuous 
external feature of well preserved mature examples. 
Internal characters: In the axial region of vertical sections the tubes have thin 
and irregularly fluctuating walls, and few or no diaphragms. The latter are com- 
plete here and the proximal end of the tube expands to full size with unnsual 
