EARLY PALEOZOIC BRYOZOA OF THE BALTIC PROVINCES. 



115 



careful description of P. gladiola applies equally well to the Russian 

 example before me, and for that reason is quoted: 



Polyzoary, consisting of a single elongated, narrow, two-edged, 

 imbranclied frond, usually curved, gradually expanding from an 

 acute point to a width of about 1 line in a length of from 1 to 28 

 lines, moderately convex, often subangular along the middle and 

 with flat slopes to the edges, which are acute. Cells oblong; 

 when perfect, nearly rectangular at their extremities; when worn, 

 one or both ends rounded; their length about twice their width, 

 6 to 8 in the length of 1 line, arranged in very regular longitudinal 

 rows, of which there are about 12 where the width of the frond is 

 1 line. The largest frond seen is 28 lines in length and IJ in 

 width at the larger extremity. 



Occurrence. — The American type was found in the 

 earliest Silurian strata equivalent to the Richmond 

 formation, on the island of Anticosti, Gulf of St. 

 Lawrence. The European specimens believed to 

 belong to the same species, occur in the Borkholm 

 limestone (F2) at Borkholm and Lyckholm, Esthonia. 



PlesiotyiJc— Cat. No. 57210, U.S.N.M. 



Fig. 43.— Ptilodic- 

 tya gladiola. 

 Tangentul sec- 

 tion, X20, show- 

 ing THE longitu- 

 dinal ARRANGE- 

 MENT OF THE ZOCE- 



cu. Borkholm 

 limestone (f2), 

 Boekholm, E s - 

 thonia. 



Genus ESCHAROPORA Hall. 



Escharopora Hall, Nat. Hist. New York, Pal., vol. 1, 1847, p. 72. — Ulrich, 

 Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 1893, p. 167; Zittel's 

 Textbook of Paleontology (Eng. ed.), 1896, p. 279. — Nickles and Bassler, 

 Bull. 173, U. S. Geol. Surv., 1900, p. 45.— Cumings, Thirty-second Ann. 

 Rep. Dep. Geol. Nat. Res. Indiana, 1907, p. 745. 



Ptilodictya (part), various authors. 



Although long considered a synonym of Ptilodictya, the species of 

 EscTiaropora form a natural assemblage related to the former genus 

 in its general zoarial and zooecial characters but differing mainly in 

 the arrangements of their apertures. In Ptilodictya the zooecial aper- 

 tures are arranged in regular longitudinal rows ; in Escliaropora their 

 arrangement is in diagonally intersecting series. The internal struc- 

 ture of the two genera is essentially the same. 



All of the species of Escliaropora are of Ordovician age while the 

 oldest known forms of Ptilodictya occur in the earliest Silurian (Rich- 

 mond) deposits. The close relationship between the two genera is 

 thus apparent from their geologic distribution, Ptilodictya being 

 undoubtedly a derivative of the earlier genus. 



Genotype. — Escliaropora recta Hall. Middle Ordovician of New 

 York and Canada. 



