74 



BULLETIN 11, TJlSriTED STATES NATIONAL MUSEUM. 



Fig. 18.— Pkotocrisina uleichi. a, portion of a 



ZOAEIUM, NATURAL SIZE; 6, ANOTHER FRAGMENT, 

 SHOWING THE NONCELLULIFEROUS SIDE, NATURAL 

 SIZE, AND ENLARGED EIGHT DIAMETERS. THE 

 MEDIAN ROW OF PORES IS MOST CONSPICUOUS; 

 C, CELLULIFEROUS SIDE OF ANOTHER FRAGMENT, 

 X 8, EXHIBITESTG THE REGULAR ARRANGEMENT OF 

 THE ZOCECIA AND ACCESSORY PORES. KUCKERS 



SHALE (C2), Baron Toll's estate, Esthonia. 



of the zoariuni. On the celluHferous face they are almost entirely 

 restricted to the middle length and occur in a unilinear series. The 

 same restriction to the mid-length is present on the noncelluliferous 

 face, where, however, the pores open at the bottom of a sulcus 

 ^ ^ extending the full length of the 



branch. Occasionally a few of 

 the same pores are found outside 

 of this middle line. 



The above description ap- 

 plies to the normal or average 

 branches. Old examples show 

 greatly thickened stems with the 

 regular arrangement of the 

 zocecial apertures and accessory 

 pores quite indistinct. When 

 compared with other members 

 of the genus, the common occur- 

 rence of the pores along a middle 

 line is the most distinctive char- 

 acter of P. ulricJd, but other fea- 

 tures are the large size of the aper- 

 tures and their regidar arrange- 

 ment in two longitudinal rows. 

 Occurrence. — Not uncommon in the Kuckers shale (C2), Baron 

 Toll's estate, near Jewe, Esthonia. 

 Coty pes.— C&t. No. 57188, U.S.N.M. 

 British Museum collection, three specimens. 



Family CERAMOPORID^ Ulrich. 



This very characteristic family of Bryozoa is well represented in 

 the Russian deposits by new or described species of all its genera save 

 two unusual types, CeramopTiylla and CJiiloporella, each of which is 

 known only from a single species. In America, specimens of cera- 

 moporoid bryozoans are often exceedingly abundant, but the collec- 

 tions from Russia have yielded comparatively few examples of the 

 rather numerous species determined. This, however, may be due 

 to a lack of systematic collecting rather than to actual scarcity of 

 material. The family is one of the most important of Paleozoic 

 bryozoans and is undoubtedly the progenitor of the equally important 

 Fistuliporidge, so prolific in Silurian, Devonian, and Mississippian 

 rocks. The Ceramoporidse are sparsely represented in the Silurian 

 and the family is essentially an Ordovician one. 



Externally a ceramoporoid may be identified by its more or less 

 oblique aperture with a portion of its margin elevated into an over- 

 arching hood known as the lunarium. This elevated portion accen- 

 tuates the obhque aspect of the aperture and often gives an imbri- 



