146 



BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 





COSCINIUM PRiENUNTIUM, new species. 

 Plate 7, figs. 5, 6; text fig. 69. 



Zoarium a bifoliate, flabellate, cribrose frond, 30 or raore ram. high 



and the same width, growing from an expanded base attached to 



foreign bodies. The individual branches are 2 mm. in width and 1 mm. 



thick. An average 

 fenestrule is broadly 

 oval in outline and is 

 2 mm. long and 1.5 

 mm. wide. Base of 

 zoarium and margins 

 of branches noncellu- 

 Hferous and finely 

 granulose. Apertures 

 subpyriform to trilo- 

 bate in outhne with a 

 distinct lunarium oc- 

 cupying the posterior 

 third or fourth. An 

 average zooecium is 

 0.24 mm. long; five 

 in 2 mm., measuring 

 lengthwise. Inter- 



zooecial spaces as wide and often wider than the zooecia, solid at 



the surface, granulose or granulostriate. 



Coscinium prsenuntium has a smaller zoarium than the later 



representatives of the genus. It differs too decidedly from other 



Ordovician forms to require comparison. 



Occurrence. — Rare in the Orthoceras Hmestone (B3), island of 



Rogo, Esthonia. 



Holotype.— Cat. No. 57243, U.S.N.M. 



Specimen and thin sections in the British Museum. 



Family ARTHROSTYLID^ Ulrich. 



Zoarium articulated, consisting of numerous subcylindrical seg- 

 ments, united into small pinnate or bushy colonies, or of continuous, 

 dichotomously divided branches; zooecia sub tubular, more or less 

 oblique, radially arranged about a central axis, and opening on all 

 sides of the segments; or one side may be noncelluliferous and longi- 

 tudinally striated. 



Both the zooecial and zoarial characters of the Arthrostylidse are 

 so distinctive that thin sections are seldom necessary for accurate 

 specific determination. It is surprising that of the 12 species of the 

 family identified in Russian strata, 10 are characteristic American 

 forms. 



Fig. 69.— Coscenium PE^NimTroM. a, tangential section, X20; 6, 



VEBTICAL section, X20. OETHOCERAS LIMESTONE (B3), ISLAND 



OF RoGO, Esthonia. 



