EAELY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 



279 



Zoarium of irregularly ramose, subcylindrical, smooth brandies, 

 ° usually 5 to 7 mm. in diameter. Zooecial apertures subangular, 

 somewhat irregularly arranged, seven to eight in 2 mm., with moder- 

 ately thick walls, ridge shaped when perfect, and with acanthopores 

 at the angles of junction. Mesopores few and irregularly developed. 



The internal structure is well illustrated in the accompanying 

 figure, which is copied from Ulrich. The zooecia are smaller than in 

 any of the other species of the genus, and this, in addition to their 

 shape, will aid in identification. 



Occurrence. — Common in the Rhinidictya bed of the Black River 

 (Decorah) shales of Minnesota; apparently rare in the Jewe beds (Dl) 

 at Paeskiill (Cat. No. 57381, U.S.N.M.), and in the Wesenberg lime- 

 stone (E) at Wesenberg, Esthonia (Cat. No. 57382, U.vS.N.M.) 



British Museum, specimen and thin section from Paeskiill, Esthonia. 



Fig. 167.— Batostoma ■winchelli spinulosum. o, a Russian example, nattjeal size; 6, tangentul 

 section, x20, showing thick "walls and fewer laegek acanthopoees than usual; c, seveeal 

 zocecia of another tangential section of the same specimen, x20, exhibiting the normal devel- 

 OPMENT OF ACANTHOPOEES NOTED IN AMERICAN EXAMPLES; d, VERTICAL SECTION, X20. WASSALEM 

 BEDS (D3), UXNORM, ESTHONIA. 



BATOSTOMA WINCHELLI SPINULOSUM Ulrich. 



Text figs. 167, 168. 



Batostoma winchelli var. spinulosum Ulrich, Geol. and Nat. Hist. Surv. Minne- 

 sota, vol. 3, pt. 1, 1893, p. 296, pi. 27, figs. 7, 8; Zittel's Textbook of Paleon- 

 tology (Eng. ed.), 1896, p. 275, fig. 459 C. 



In the typical form of this species the acanthopores are small or 

 only of medium sii^e, and are numerous enough to occupy nearly all 

 the junction angles. The present variety was distinguished by Ulrich 

 to include those specimens having the same general zoarial and 

 zooecial characters except that the acanthopores are much stronger 

 and the zooecia are a trifle larger. Tangential sections prepared 



