274 BULiLETIN 77, UNITED STATES NATIONAL MUSEUM. 



apertures. Diaphragms are very remote or wanting in the axial region, and not 

 numerous even in the peripheral portion. Here each tube presents from one to five, 

 separated by intervals of from one-half to one tube diameter. In the mesopores, 

 which appear to be very short, the diaphragms are much closer, with three or four in 

 0.5 mm. In the central part of transverse sections the tubes are conspicuously divided 

 into a large and small set, both having very thin walls. 



Occurrence. — The American types are from the Rhirddictya bed of 

 the Black River (Decorah) shales of Minnesota. In Russia the species 

 is known only from the Wassalem beds (D3) at Uxnorm, Esthonia. 



Plesioty2Je.—Csit. No. 57377, U.S.N.M. 



Thin sections of the Russian type are in the collections of the 

 British Museum. 



BATOSTOMA FERTn,E Ulrich. 

 Text fig. 163. 



Batostoma fertilis Ulrich, Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. Minne- 

 sota, 1886, p. 92. 



Batostoma fertile Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 

 1893, p. 290, pi. 25, figs. 1-11; Zittel's Textbook of Paleontology (Eng. ed.), 

 1896, p. 275, fig. 459 B. 



Original description. — Ulrich thus describes this species : 



Zoarium attaining a large size, 50 to 100 mm. in height, consisting of strong, irregu- 

 larly thickened, more or less compressed branches that divide without regularity; 

 thickness of branches 5 to 25 mm., width 8 to 30 mm. Zooecial apertures varying 

 according to the size and number of the mesopores and the thickness of the walls, 

 from polygonal to circular. In some specimens and portions of others mesopores are 

 exceedingly few and the zooecial walls thin and generally in contact at all sides; in 

 the majority of examples mesopores are moderately abundant and the walls thicker, 

 but the zooecial apertures are still polygonal or at any rate most of them subangular. 

 From this, the typical form, we can trace the variations by small degrees into a form 

 which, for the sake of reference, may be designated as var. circulare. In this the zooe- 

 cial apertures are almost perfectly cu'cular, inclosed by a raised rim or peristome, and 

 largely separated from each other by depressed interspaces. * * * Interspaces 

 occupied by mesopores varying considerably in size and shape. Their mouths are 

 commonly closed by a calcareous plate in which a variously situated rounded opening 

 may be observed. When the preservation is unusually favorable the surface of the 

 plate is studded with very minute papillse representing the terminations of exceed- 

 ingly small foramina. Acanthopores between one and two to each zocecium, but 

 very small and only in rare instances distinguishable at the sxirface. At intervals 

 of 3 or 4 mm. occur clusters of zooecia a little larger than the average, and in the center 

 of these usually small substellate maculse. Between eight and nine of the average 

 zooecia in 3 mm. 



Internal characters: In vertical sections the tubes have thin and somewhat irregu- 

 larly fluctuating walls in the axial region. Their course to the surface is gently curved 

 throughout, and as they near the same their walls are appreciably thickened, while 

 mesopores, whose number varies greatly in different specimens, are abruptly devel- 

 oped. The mesopores may be constricted at the points where they are intersected 

 by the diaphragms. The latter are often thickened circumferentially, and vary some- 

 what in the number occurring in a given space, seven and eleven in 1 mm. being 

 the extremes so far noticed. In the axial region diaphragms are very far apart or 

 are wanting entirely, but in the peripheral portion the average distance between 

 them is about equal to half their diameter. Specimens more than 12 mm. thick 

 consist of two or more layers of tubes. 



