30 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



Genus GONOPEUM Gray, 1848 



This genus is especially characterized by the development of triangu- 

 lar cavities on the surface of the gymnocyst at its proximal corners 

 ("interopezial cavities"). In the early growth of the zooecium the small 

 gymnocyst is smooth, then calcified w^alls begin to enclose a triangular 

 space, sometimes in each basal corner, sometimes in only one corner, and 

 very frequently they may be wanting over a large portion of a colony. 

 As calcification becomes complete, triangular or rounded knobs, with a 

 small membranous aperture, are formed. These may even become closed 

 and also they may be fused across the basal part of the zooecium to form 

 irregular quadrangular lumps or knobs. Avicularia and mural spines are 

 wanting. (See Marcus 1937:36, and Osburn 1940:350). Genotype, 

 Flustra lacroixii Audouin, 1826. 



Gonopeum commensale Kirkpatrick and Metzelaar, 1922 

 Plate 2, figs, 12, 13, 14 and 15 



Kirkpatrick and Metzelaar, 1922:985. 



Marcus, 1937:35, 1938:16, 1939:126 (discussion). 



The zoarium usually encrusts shells, especially gastropod shells in- 

 habited by hermit crabs ; white in earlier stages, becoming yellowish and 

 finally brown ; multilaminar. 



The zooecia are rather regular in arrangement, roughly quadrangu- 

 lar or elongate-hexagonal, the outlines marked by a very distinct dark 

 brown line. The membranous ectocyst covering the frontal surface is 

 thickly studded with chitinous, villose spinules, especially around the 

 border; these spinules are semierect, pointed toward the center of the 

 zooecial area, and do not occur on the mural rim. The zooecial walls 

 are heavily calcified and the mural rim as well as the descending crypto- 

 cyst is granulated. The opesia is ovoid in form and the operculum well 

 chitinized, with a somewhat heavier border, yellowish in color. 



Originally found at a number of localities in northwest Africa. Mar- 

 cus (1937:36) records it from various places in Bahia de Santos, Brazil, 

 and gives an excellent account of it. 



There is much variation in the form of the tubercles and they may 

 be single or double, large or small, and may often be wanting over con- 

 siderable areas of a colony. The chitinous ectocystal spinules also show 

 much variation, usually numerous in our material, but sometimes want- 

 ing altogether. Kirkpatrick and Metzelaar did not mention them in 



