28 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



and Fraile Bay; Port Culebra, Costa Rica; Secas Islands and Bahia 

 Honda, Panama; James, Hood, Indefatigable and Chatham Islands, 

 Galapagos, the greatest depth being 40 fms. 



Membranipora pachytheca new species 

 Plate 2, figs. 2 and 3 



Zoarium encrusting shells, white in the young, brownish in color 

 when fully developed. The zooecia are large (average about 0.85 mm 

 long, but ranging from 0.65 to 1.10 mm, and in width ranging from 

 0.45 to 0.65 mm) ; ellipsoid with the distal end evenly rounded and 

 slightly elevated; distinct; the walls very thin; opesia occupying all of 

 the front ; no evident gymnocyst ; a slight horizontal cryptocyst, usually 

 in the proximal corners but often there is no evidence of it. The mural 

 rim is smooth and exceedingly thin, there is no evidence of a descending 

 crj^ptocyst and the horizontal cryptocyst is minute and perfectly smooth. 

 The frontal ectocyst is thick, pale brownish, and covers the whole of the 

 frontal surface, forming a thin brown line above the adjoining mural 

 rims and continued more heavily around the distal end of the zooecium. 

 The operculum is heavily chitinized and brownish in color, slightly arcu- 

 ate in cross-section, very large (0.25 to 0.30 mm in width by 0.25 to 0.30 

 mm in length) thinner at the edges, with a sclerite on either side a little 

 way within the margin. In the side walls there are 4 multiporous rosette 

 plates, while in the distal wall there are numerous single pores which 

 form a band across it at its middle. The tentacles are numerous, about 20. 

 There are no avicularia and no ooecia; developing ova can be observed 

 in the body cavity. 



This is an unusual appearing species, looking at first sight like an 

 encrusting Alcyonidium; on being calcined the thin walls and large opesia 

 suggest Aplousina but there is no evidence of endozooecial ovicells. The 

 negative characters, such as the absence of the gymnocyst, the vestigial 

 cryptocyst, the absence of spines, denticles, avicularia and ooecia, the re- 

 duced calcification and the nature of the communication pores all appear 

 to indicate Membranipora as the proper genus. 



The most striking characters are the large, arched, leathery opercul- 

 um, the rounded distal ends of the large zooecia and the unusually thin 

 walls. 



Type, AHF no. 10. 



Type locality. Canoe Bay, Alaska, 40 fathoms, on shells, several 

 colonies, one more than an inch across (Alaska Crab Investigation). 



