BEYOZOA. 297 



Batostoma minnesotense.l 



Batostoma minnesoten'sb, n. sp. 



PLATE XXVI, FIGS. 38-40; PLATE XXVII, FIGS. 9-15. 



AmplexQpora superba Ulbich, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. Minn., p. 92. 



(Not Foord, 1883, Coatri. Micro-Pal. Cambro-Sil. Eocks, Can., p. 36.) 



Zoarium ramose, above the medium size for the genus; branches without mon- 

 ticules, subcylindrical, bifurcating at rather long intervals, averaging 9 or 10 mm. 

 in diameter, but varying .between the extremes of 7 and 15 mm. Zogecial apertures 

 subangular, with walls of moderate thickness, arranged in regular curving series 

 about clusters of orifices that are in most cases decidedly larger than the average; 

 of the latter sometimes nine, more often ten, occup in 3 mm. Prominent acantho- 

 pores a,t all the angles of junction, and in many cases another is placed between the 

 angles. These at all times occupy the summit or center of the walls and in no case 

 cause irregularities in the form of the zocecial apertures. Mesopores very few, 

 scattered at random among the larger apertures. 



Internal characters: In tangential sections the walls are nearly uniformly thick, 

 with the angles of junction often appearing as open (pi. XXVII, fig. 15). In other 

 cases the angles are occupied by dark spaces looking more like the usual appearance 

 of acanthopores. A more typical phase of the species is shown in figs. 9 and 10, 

 representing parts of a section of an excellently preserved example. In this we 

 have more abundant acanthopores and the cavity in these is unusually large, while 

 many of the angles are occupied by open spaces similar to those shown in fig, 15. 



Jn vertical sections the tubes are provided with thin wavy walls in the axial 

 region, where they are also a little irregular and generally entirely without dia- 

 phragms, the latter first making their appearance as the tubes bend injio the 

 peripheral region. In the outer region the walls are much thickened and in places 

 distinctly traversed longitudinally. by acanthopores. The mesopores are but seldom 

 observed, have few diaphragms and appear to be in part filled with solid tissue. The 

 arrangement of the diaphragms in the zocecial tubes varies somewhat in difiierent 

 sections. Figures 11 and 13 represent extremes in this respect. 



This species, though closely related to B. winchelli, is readily distinguished 

 externally by its larger size and slightly larger and more regularly arranged zocecial 

 apertures; internally by the wavy walls and the absence of diaphragms in the axial 

 region. Foord's Amplexopora superba, to which I at first referred this species, is 

 probably congeneric, but distinguished specifically by having nearly straight instead 

 of wavy walls to the axial tubes, and a tuberculated surface. 



Formation and locality.— 'Sot rare in the middle third of the Trenton shales at Minneapolis, St. 

 Paul and other localities in Minnesota, 



Mus. Beg. Nos. 5996, 5998, 7592, 7668, 8093. 



