EARLY PALEOZOIC BEYOZOA OF THE BALTIC PEOVINCES. 189 



but later reduced to synonymy. The characters of H. insignis are 

 undoubtedly those of young examples of H. subramosa. 



Occurrence. — The American occurrences are in the Black River 

 and earliest Trenton formations of Minnesota and Iowa. In Russia, 

 the species is not uncommon in the Kuckers shale (C2) at Reval, 

 Esthonia. 



Plesiotype.—Csit. No. 57274, U.S.N.M. 



A specimen and thin sections from the Kuckers shale, Reval, 

 are in the collections of the British Museum. 



Genus HOMOTRYPELLA Ulrieh. 



Eomotrypella Ulrich, Fourteenth Ann. Rep, Geol. Nat. Hist. Surv. Minnesota, 

 1886, p. 83.— Miller, North Amer. Geol. and Pal., 1889, p. 310.— Ulrich, 

 Geol. Surv. Illinois, vol. 8, 1890, pp. 370, 412; Geol. and Nat. Hist. Surv. 

 Miimesota, vol. 3, pt. 1, 1893, p. 228. — Simpson, Fourteenth Ann. Rep. 

 State Geologist for the year 1894, 1897, p. 586. — Nickles and Bassler, 

 Bull. 173, U. S. Geol. Surv., 1900, p. 29. 



Three separate sections of this genus are represented in the Black 

 River and earhest Trenton rocks of North America. The first 

 comprises the typical species and consists of stout, ramose branches 

 with direct zooecia, numerous acanthopores and mesopores, and 

 long mature regions. The second section has short mature regions 

 and obhque apertures, while the third consists of species with a mass- 

 ive zoarium and strong acanthopores, hitherto referred to Prasopora. 

 All three sections are represented in the Russian Ordovician by 

 typical American species. 



In growth and several other characters Eomotrypella is quite similar 

 to Homotrypa, but it differs conspicuously in the presence of numerous 

 tabulated mesopores. 



Genotype. — Homotrypella instabilis Ulrich. Middle Ordovician 

 (Black River) of the Mssissippi Valley. 



HOMOTRYPELLA INSTABILIS Ulrich. 



Text figs. 101, 102. 



Homotrypella instabilis Ulrich, Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. 

 Minnesota, 1886, p. 83; Geol. and Nat. Hist. Surv. Minnesota, vol. 3, 1893, 

 p. 229, pi. 18, figs. 9-20. — Simpson, Fourteenth Ann. Rep. State Geologist of 

 New York for the year 1894, 1897, p. 586, figs. 168, 169. 



Specimens which fall within the range of characters presented by 

 this very abundant Black River fossil are frequent in the Kuckers 

 shale. As indicated by the specific name, the species is somewhat 

 variable, yet almost every phase noted in the American specimens 

 has been duphcated in the Russian examples. In figure 101 I have 

 introduced a few of Ulrich's excellent illustrations of the species, but 

 as these show the mature characters more clearly, another set of 

 drawings (fig. IO22) to illustrate the young stages, is added. Ulrich 



