82 BULLETIN 16 5, UNITED STATES NATIONAL MUSEUM 



The areolar pores do not surround the frontal only, for they 

 occur also around the distal portion of the peristome. By abrading 

 the surface, it can be observed that the distal half of each zooecium 

 is surrounded by dietellae; these correspond to the distal areolar 

 pores. 



The largest colony observed measures 3 cm in length and con- 

 tains five superposed lamellae. As it surrounds some fragment that 

 rested on the sea bottom, sedimentation must have been very slow. 



Affinities. — The appearance in the Vincentown limesand of this 

 Recent equatorial genus is quite remarkable. The general structure 

 of the cheilostomatous Bryozoa is already quite complicated in the 

 Upper Cretaceous, but the simpler forms are more abundant while 

 others are very rare. We note finally that this genus still exists 

 in the Gulf of Mexico. 



Hippaliosina aspera differs from the other known species in the 

 smallness of its avicularia and of its ovicells. 



The geographic distribution of the species of a genus of cheilostom- 

 atous Bryozoa is controlled by capricious biologic conditions. Thus 

 we note that Hippaliosina, arising in the Vincentown limesand of 

 America, is absent from this country during the Eocene and 

 Oligocene but reappears in the Upper Miocene and persists in the 

 Gulf of Mexico. In Europe, on the contrary, it appeared in the 

 Eocene, persisted through the Oligocene and the Miocene, and 

 disappeared during the Pliocene. 



The species of Hippaliosina are of shallow water, 30 to 50 meters 

 deep, but while they are known to ascend to a greater depth and 

 endure a temperature of 12° to 25° C. in the equatorial zone, they 

 cannot do this in another zone. Also by the aid of these species, 

 Canu, 1918, has shown that the contraction of the tropical zone in 

 the geologic series can be followed. 



Occurrence. — Vincentown limesand : Timber Creek and Mullica 

 Hill, N.J. (Gabb and Horn) ; rare at Vincentown and near Black- 

 woodstown, N.J., and and at Noxontown Millpond, Del. Eocene 

 (Aquia) : Upper Marlboro, Md. 



Plesiotypes.—U.S.'NM. No. 73912. 



Family RETEPORIDAE Smitt, 1867 



PSILOSECOS, 19 new genus 



Reteporidae( ?) in which the ovicell is hyperstomial, closed by the 

 operculum. The frontal is smooth and bears two to four sublateral 

 pores. The apertura is lepraliform provided with a mucron trans- 

 formed into a lyrula and with a distal peristomial avicularium. 



i 8 From i/a\6s, bare + o-tjkos, small case; referring to the aspectfcf the frontal. 



