NO. 1 OSBURN : EASTERN PACIFIC BRYOZOA CHEILOSTOMATA 95 



Family Arachnopusiidae JulHen, 1888 



An arched calcified frontal shield or pericyst which is perforated by 

 numerous large pores above the membranous ectocyst. The pericyst is 

 formed by irregular projections originating from the lateral and proximal 

 margins. Levinsen (1909:160) states that the projections in Arachno- 

 pusia are at first hollow spines which later become solid. In the other 

 two genera here considered there is no evidence of hollow spines at any 

 time. 



There is much uncertainty whether these two genera belong with 

 Arachnopusia, and also whether the family is properly placed. It is pos- 

 sible that it should be included among the cribrimorphs, but the pericyst 

 is not formed of parallel or radial costae. 



Genus EXECHONELLA Canu and Bassler, 1927 



"The frontal pores are orbicular. A peristome very much developed, 

 surrounds an orifice closed by a true operculum. The ectocyst is hidden 

 under the frontal" (Canu and Bassler, 1926:4). Genotype, Hiantopora 

 ma:^nff MacGillivray, 1895. 



The external appearance is that of a member of the Ascophora, but 

 careful dissection exposes the ectocyst which covers the full breadth of 

 the opesia beneath the pericyst. The dorsal wall is provided with tubular 

 processes for attachment. 



Exechonella antillea (Osburn), 1927 



Plate 10, figs. 9 and 10 



Lepralia antillea Osburn, 1927 :128. 

 Exechonella pumicosa Canu and Bassler, 1928:70. 

 Exechonella antillea, Osburn, 1940 :366. 



Zoarium encrusting on shells, corals, etc., forming a coarse yellowish 

 or grayish layer; attached by dorsal processes, one or more on each zo- 

 oecium. Zooecia large, 0.70 to more than 1.00 mm in length by 0.60 to 

 0.70 mm in width ; well separated by deep grooves even in older stages. 

 The whole area of the gibbous pericyst is coarsely perforated, each pore 

 being surrounded by a broad collar. A thick-walled peristome, usually 

 considerably elevated but lower on the proximal border, often bearing 

 tubercles, and occasionally the whole rim flared outward. The aperture 

 is large, about 0.20 to 0.25 mm in either dimension, varying in form but 

 usually slightly quadrate with the corners rounded. The operculum is 



