NO. 2 OSBURN: eastern pacific BRYOZOA CHEILOSTOMATA 277 



Key to Species of Hippothoa 



1. Zoarium multiserial, often covering large areas .... hyalina 

 Zoarium uniserial, with lateral branches 2 



2. Zooecia with very long basal tubular prolongations . . flagellum 

 Basal prolongations usually not longer than the zooecial body . 3 



3. Zooecia large, with a broad calcareous expansion along the . . 



sides expansa 



Zooecia much smaller, the lateral expansion narrow or ... . 

 wanting divaricata 



Hippothoa hyalina (Linnaeus), 1758 

 Plate 30, figs. 1-5 



Cellepora hyalina, Linnaeus, 1758:1286. 

 Schizoporella hyalina, Hincks, 1884: 17. 

 Schizoporella hyalina, Robertson, 1908 :289. 

 Schizoporella hyalina, O'Donoghue, 1923 :35. 

 Hippothoa hyalina, Canu and Bassler, 1923 : 92. 

 Hippothoa hyalina, O'Donoghue, 1925 :101 ; 1926:54. 

 Hippothoa hyalina, Hastings, 1930:720. 



Zoarium encrusting on anything that will afford attachment, often 

 covering large areas on shells and broader algae; at first a smooth, 

 glistening, more or less hyaline layer, it may become multilaminar and 

 piled up into irregular masses with a rough surface, or losing its hyalinity 

 may be chalky white. 



The zooecia in the younger stage are more or less terete, with narrow, 

 elongate fenestrae partially separating them, transversely ribbed or lined, 

 smooth and glistening, imperforate. The aperture is rounded or short- 

 ovate, with a broad, shallow sinus, the peristome thin and slightly ele- 

 vated. A low, pointed umbo is often present just proximal to the aperture. 



The ooecia are large and conspicuous, usually borne on somewhat 

 dwarfed gonoecia which stand up more or less erect among the zooecia. 



There is so much variability in this species that it often presents a 

 difficult problem to the beginner, but marginal zooecia will usually show 

 the essential characters. A number of varieties have been given names. 



It is a truly cosmopolitan species, occurring around the world and 

 from the Arctic, where it is often excessively abundant, to the tropics. 

 It has been reported by everyone who has studied Pacific coast Bryozoa, 

 from Alaska to southern California, and Hastings recorded it from the 

 Galapagos Islands. 



In the Hancock collections it has been noted at 69 stations all the 

 way south to Peru and the Galapagos Islands. 



