280 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



It is a widely distributed species and is known as a fossil as far back 

 as the Miocene. The only record for the Pacific coast of America is 

 that of Canu and Bassler "Galapagos Islands, D.2813." It has not 

 appeared in the Hancock collections. 



Genus TRYPOSTEGA Levinsen, 1909 



"The zooecia with scattered pores and a compound operculum. The 

 ooecia covered by dwarf zooecia with scattered pores. No avicularia" 

 (Levinsen 1909:280). Genotype, Lepraliavenusta Norman, 1864. 



A zooeciule is usually present at the distal end of each normal zooe- 

 cium in the form of a small quadrangular chamber, but they are often 

 wanting, sometimes over considerable areas ; also the zooeciule forms a 

 covering layer over the ooecium. The nature of the zooeciule or dwarf 

 zooecium has been in doubt and Levinsen definitely states "no avicularia." 

 The rounded apertures of the zooeciules in T. venusta are very minute, 

 only about 0.03 to 0.04 mm in diameter and appear to have no mandibles, 

 but in T. claviculata (Hincks) there are small spatulate mandibles. The 

 zooeciules may therefore be interpreted as avicularian kenozoecia and 

 in the type species, venusta, the avicularium is vestigial. 



Trypostega venusta (Norman), 1864 

 Plate 30, fig. 10 



Lepraliavenusta Norman, 1864:84. 

 Trypostega venusta, Canu and Bassler, 1930:14. 

 Trypostega venusta, Hastings, 1930 :720. 

 Trypostega vetiusta, Mzrcws, 1938:35 (synonymy). 



Zoarium encrusting, sometimes multilaminar, white, smooth and 

 glistening. The zooecia are somewhat rhomboid, a little inflated, with 

 numerous pores, sometimes with a small rounded umbo proximal to the 

 aperture ; 0.40 to 0.45 mm long by 0.26 to 0.30 mm wide. The aperture 

 is pyriform, rounded distally to the strong, triangular cardelles and 

 behmd these is a broad, somewhat triangular sinus; aperture length 

 0.10 mm, width 0.08. The zooeciules are usually situated at the distal 

 ends of the zooecia, but sometimes between them. Occasionally the zooe- 

 cuiles may be nearly as large as the normal zooecia, but without any 

 increase in the size of the minute aperture. 



The ooecia are deeply immersed, scarcely raised above the level of 

 the crust, covered by the enclosing zooeciule, about 0.25 mm broad by 

 0.20 mm long, porous and surmounted by a low umbonate process. 



