ART. 13 BRYOZOAN FAUNA CANU AND BASSLER 25 



The avicularia considered two by two are perpendicular. But on 

 the very curved or small parts of the colony this geometric arrange- 

 ment is changed. On the much calcified zooecia the avicularia have a 

 ver}^ reduced shape, and the utility of their interposition there 

 appears doubtful, or at least very slight use. 



The intensity of the life is very great in the tropical zone. The 

 least substratum is watched not only by the larvae of bryozoa, but 

 also by the corals and by the spores of Lithothamnion. While the 

 colony is living it is clean and never incrusted. "We may suppose 

 that the defensive role of the frontal and more particularly of the 

 operculum is held by the avicularia when the cells are closed and 

 by the tentacles when they are open. 



Reproduction must occur as in Gryptomla, because here also there 

 are no ovicells. 



Occurrence. — Galapagos Islands, D. 2815, 



Coty pes. ~C2it. No. 8494, U.S.N.M. 



Family PETRALIIDAE Levinsen, 1909 



PACHYCLEITHONIA, new genus 



Greek: Pachys, thick; cIeithon=Q\osure; referring to the thickness of the 

 operculum. 



The cells are gigantic in size. The frontal is a tremocyst not super- 

 posed on an olocyst. The aperture is arranged in the peristomie 

 bearing two large condyles and two small symmetrical cups. 



Genotype. — Pachycleifhonia nigra, new species. Recent (Pacific). 



We have classed this genus in the Petraliidae provisionally by sim- 

 ple analogy. The large size and the form of the cells are those of 

 Goleopora. The peristomie presents the prox- 

 imal undulations of certain Petraliella. 



PACHYCLEITHONIA NIGRA, new .species 



Plate 4, Figures 9-13 



Description. — The zoarium incrusts shells. 

 The zooecia are unusually large, distinct, sepa- 

 rated by a deep furrow, very elongated, ellip- 

 tical; the frontal is a simple tremocyst with figdre 6. — pachyclei- 

 small pores; the ectocyst is thick and Hack. l^°^l^ J^^d^'svec^Z 

 The peristomie is tubular, somewhat deep, per- sketch of the orifice 

 pendicular to the zooecial plane ; it bears on the ^^ ^Brnw ^Sdyles • 

 interior two large oblique condyles and two g, cop; m, proximal 

 small lateral cups. The peristome is thin, mucron 

 smooth, complete; the peristomice is semicircular distally and 

 bears in its proximal portion a rounded mucron and two sublateral 

 denticles. The apertura is limited by the anter, the condyles, the 

 cups, and the mucron. 



