114 



BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



PTILODICTYA FLABELLATA Eichwald. 



Text fig. 42. 



Ptilodictya flabellata Eichwald, Lethsea Rossica, vol. 1, 1860, p. 389, pi. 24, figs. 



10 a, b. 

 Cfr. Ptilodictya expansa Hall, Twelfth Ann. Rep. Indiana Geol. Nat. Hist., 1883, 



pi. 12, figs. 2, 3. 



Although this species is briefly described by Eichwald, his figures 

 are sufficient to show that it is undoubtedly a Ptilodictya closely 

 related to the typical earliest Silurian forms. A very similar, perhaps 

 identical American species from the CHnton formation of Ohio, has 

 been illustrated by Hall as Ptilodictya expansa. 



Although specimens of Ptilodictya fiabellata have not occurred in 



the collections be- 

 ^ fore me, I have no 



hesitancy in includ- 

 ing it as a valid spe- 

 cies. Eichwald re- 

 cords the species as 

 from the compact 

 Ordovician (Ortho- 

 ceratite) limestone, 

 near Hohenholm, 

 island of Dago, 

 which will place it in 

 either theLyckholm 

 or Borkliolm divi- 

 sion of formation F. For various reasons, chiefly on account of its 

 Silurian affinities, and its geographic location, I would regard Ptilo- 

 dictya fiabellata as belonging to the same fauna holding HaUopora 

 elegantula, Sceptropora f acuta, Lichenalia concentrica, etc., namely, 

 that of the Borkholm horizon. 



Occurrence. — Hohenholm, island of Dago, probably in the Borkholm 

 limestone (F2). 



PTILODICTYA GLADIOLA Billings. 



Text fig. 43. 



Ptilodictya gladiola Billings, Cat. Sil. Foss. Anticosti, 1866, p. 10. 



Ptilodictya lanceolata Eichwald (not Goldfuss), Lethsea Ross., vol. 1. 1860, p. 388. 



An elongated, lamellate, slightly curved bifohate bryozoan with the 

 cells arranged in longitudinal rows, has been described by Eichwald 

 as Ptilodictya lanceolata (Goldfuss)^ and recorded as from the Ordo- 

 vician Hmestone of Lyckholm, as well as from various Silurian 

 localities. The Ordovician specimens belong, in all probability, to 

 the form described by Billings as Ptilodictya gladiola, which differs 

 from typical P. lanceolata mainly in having smaller zocecia. Billings's 



Fig. 42.— Ptelodictta flabellata. a, zoakium, natueal size, 



PARTED ALOKG THE MESLAL LAMINA; 6, VIEW ENLAEGED, SHOWING 

 LONGITUDINAL ARRANGEMENT OF ZOCECLA. "CALCAIEE COMPACTE A. 



Oethoceeatites/' island of Dago, near Hohenholm. (After 

 Eichwald.) 



