206 BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 



Occurrence. — Pleistocene: Santa Monica (Rustic Canyon), California (very 

 rare) . 



Habitat. — Arctic Ocean: Finmark, Spitzberg, Kara Sea (166-216 meters) , Green- 

 land, Jean Mayen (160-180 meters), Sea of Barents, Iceland (162 meters). Atlantic: 

 Scandinavia (6-24 meters), Demnark (13-18 meters), England, Labrador (24 

 meters), Canadian coast (11-97 meters), United States to the fortieth parallel. 

 Pacific: Alaska and California. 



Verrill has observed this species at 56 meters with a temperature of 6.1° C. 



Pimoiype.— Cat. No. 68754, U.S.N.M. 



Family TRETOCYCLOECIIDAE Canu, 1918. 



Genus TRETOCYCLOECIA Canu, 1919. 



(For description, see Bulletin 106, U. S. National Museum, p. 826.) 



TRETOCYCLOECIA TORTILIS Lonsdale, 1845. 



Plate 28, figs. 1-12. 



1845. Heteropora loTlilis Lonsdale, Report on the Corals from the Tertiary formation of North 

 America, Quarterly Journal Geological Society London, vol. 1, p. 500, text figure. 



1857. Heteropora tortilis Tuomey and Holmes, Pleiocene Fossils from South Carolina, p. 16, pi. 4, 

 figs. 15, 16. 



1862. Multicrescis tortilis Gabb and Horn, Monograph Polyzoa Secondary and Tertiary formations 

 North America, Journal Academy Natural Science Pliiladelpliia, ser. 2, vol. 5, p. 178. 



Structure. — The zoarium is rarely globular but is almost always irregularly 

 cylindrical, branched, attached to the radicells of algae. The ovicell is subor- 

 bicular and regularly perforated by the tubes. It is rather deep and of variable 

 dimensions. At the exterior surface the walls of the tubes are thin or thick. The 

 mesopores are rare on certain branches, abundant in groups on others. Tliis 

 irregularity must correspond to conditions of equilibrium which we still do not 

 comprehend very well. 



In longitudinal sections the tubes are cylindrical, bifurcating at all heights; 

 their walls are vesicular. The mesopores are irregularly distributed between the 

 orifices. 



In transverse sections the tubes arc polygonal at the center of the zoarium. 

 The mesopores are alwaj's rather short. 



In tangential sections the zooecial walls are thick. The interior walls are 

 strongly calcified and appear as thin black lines separated by large clearer spaces 

 corresponding to a less dense calcification. 



This is one of the most showy species of the American Miocene. 



Occurrence. — Miocene: Yorktown, Williamsburg, and 3 miles southwest of 

 Petersburg, Virginia (common) ; Smith's Goose Creek, South Carolina. 



Plesiotypes.—C&t. No. 68755, U.S.N.M. 



TRETOCYCLOECIA AVELLANA, new species. 



Plate 27, figs, 5-11. 



Description. — -The zoarium is free, spherical, born on a flat surface, and of the 

 size of a hazel nut, simple or lobed. The tubes are cylindrical, branched at all 



