108 



BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



Fig. 39.— Scenellopoea socialis. a and &, copy of Eich- 

 wald's views of Ceramopoka socialis; a, zoaeium, nat- 

 ural SIZE, INCRUSTING AN ECHINOSPHEEITES; 6, ONE OF THE 

 GROUPS OF ZOCECIA OF THE SAME, E1W.ARGED. ECHINOS- 

 PHERITES LIMESTONE (CI), PULK:0"WA, GOATERNMENT OF ST. 



Petersburg. 



SCENELLOPORA SOCIALIS (Eichwald). 



Text fig. 39. 



Ceramopora socialis Eichwald, Lethsea Rossica, vol. 1, 1860, p. 412, pi. 26, fig. 21. 



A single well-preserved specimen incrusting an Echinosplierites in 

 the collection before me agrees so well with Eichwald' s figure of 

 Oeramopora socialis that I have no doubt of its identity. The first 

 clue to the identification of this species is the distinctness of the sev- 

 eral groups of zooecia with their central, solid areas, growing together 

 as a parasitic expansion. Each of these groups, when magnified, is 

 ^ seen to consist of a ma- 



_^:rr"'V[^i^_^ ^ cula free from cell open- 



ings, from which zooecia 

 with strongly elevated lu- 

 naria radiate. Thelunaria 

 encircle theposterior three- 

 fourths or more of the 

 zooecial apertures, and are 

 distinctly arched. Eich- 

 wald's figure of the surface 

 enlarged is incorrect in- 

 showing the elevated lu- 

 narial walls as completely 

 surrounding the cell opening. Measuring along one of the radiating 

 rows of zocecia, about four apertures occur in 2 mm. 



The incrusting zoarium of small groups of zooecia with well-devel- 

 oped, arched lunaria will readily distinguish this from all associated 

 bryozoans. 



Occurrence. — Apparently rare in the Echinosplierites limestone 

 (Cl) at Poulkowa and Katlino, government of St. Petersburg. 

 Plesiotype.— Cat. No. 57207, U.S.N.M. 



Family FISTULIPORID^ Ulrich. 



This family comprises a number of genera quite similar in their 

 general characteristics to the members of the Ceramoporidse, but dif- 

 fering conspicuously in having the zooecial interspaces occupied by 

 vesicular tissue. This difference is not merely one of convenience in 

 classification but is a natural one, as shown by the history of the two 

 families. The Ceramoporidai are almost restricted to the Ordovician, 

 while the Fistuliporidse are highly characteristic of the later Paleozoic 

 rocks. With the exception of one or two undescribed primitive spe- 

 cies of Fistulipora in the Middle Ordovician strata of the Appa- 

 lachian Valley, the following species are the only Ordovician repre- 

 sentatives of the family. Each, as would be expected, is a primitive 

 member of its genus. 



