BRYO?;OA. 299 



Hemiphragma.l 



Genus HEMIPHRAGMA, n. gen. 



Batostoma (part.) Ulkioh, 1890. Geol. Surv. 111., vol. viil, p. 379. 



Zoaria like those of Batostoma save in this, that the diaphragms in the periph- 

 eral part of the zocecial 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 

 Delafleld and Iron Ridge, Wisconsin, Unfortunately, the Bryozoa which occur so 

 abundantly at those localities do not preserve the internal cTiaracters, 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 diflference be- 

 tween the two genera, we are obliged to place them together because of their 

 marked agreement in all other respects. 



Hemiphkagma irrasum Ulrich. 



PLATE XXIV, FIGS. 5-19. 



Batostoma irrasa TDlkich, 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. Zooecia 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 zooecia may be of 

 larger size than elsewhere; seven to nine in 3 mm. 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 zooecium, 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 unusual 



