EAKLY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 241 



BYTHOPORA SUBGRACILIS (Ulrich). 



Text figs. 135, 136. 



Homotrypella? subgracilis Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, 

 pt. 1, 1893, p. 230, pi. 26, figs. 10-16. 



The author of this species referred it doubtfully to Homotrypella 

 because the preservation of the internal structure was such that the 

 cystiphragms were thought to have been destroyed. Better pre- 



FlG. 135.— BYTHOPORA SUBGEACILIS. O, AN ORDINAKY FRAGMENT, NATURAL SIZE; 6, SURFACE OF SPEa- 

 MEN, X9; C, TANGENTIAL SECTION OF A POORLY PRESERVED FRAGMENT, X18; d, VERTICAL SECTION, X18. 



Rhinidictya bed OF Black River (Decorah) shales, St, Paul, Minnesota. (After Ulrich.) 



served examples from the type locahty have shown that cystiphragms 

 are entirely wanting and that generically the species differs in no 

 way from the other large forms of BytJiopora. The identification of 

 this species in the Russian strata is based upon several well-pre- 

 served specimens, agreeing in 

 all respects with the typical 

 Minnesota examples. 



The zoarium of Bythopora 

 subgracilis is of small, ramose, 

 subcylindrical, smooth 

 branches 2 to 4 mm. in diam- 

 eter. The zooecial apertures 

 are oblique or long drawn 

 out in young examples and 

 more direct in older forms, 

 eight in 2 mm. In the early 

 stages acanthopores are few, 

 but as the apertures become direct numerous small acanthopores are 

 developed. Mesopores are about as numerous as the zocecia, which 

 they often resemble so closely that it is difficult to distinguish them. 

 Diaphragms are entirely wanting, as shown in the vertical sections 

 figured herewith. 





Fig. 136.— Bythopora subgracilis. a and 6, tangen- 

 tial AND vertical SECTIONS, X20, OF A "WELL- 

 PRESERVED Russian example. WasSalem beds 

 (D3), Uxnorm, Esthonia. 



