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ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



membrane on the distal side. They are very variable, frequently fusing 

 across the end of the zooecium and occasionally they are cornuate, ex- 

 tending forward with the points curved toward each other, and more 

 rarely a third tubercle is developed between these in the midline. A short 

 gymnocyst is sometimes present and the cryptocyst, with lateral spinules 

 is usually well developed at the proximal end. 



Found wherever Sargassum drifts over the warmer seas ; along shore 

 on the Atlantic coast from North Carolina to Brazil; on the Pacific 

 coast from California to Peru and the Galapagos Islands; southern 

 Japan, Indian Ocean and the East Indies. 



Dredged in shallow water, usually on algae, by the Hancock Expedi- 

 tions at numerous stations from California to Peru. 



•s^ Membranipora perfragilis (MacGillivray), 1881 

 Plate 2, fig. 8 



Biflustra fragilis MacGillivray, 1869:138. 



Bifiustra perfragilis MacGillivray, 1881 :27 (changed the name). 

 Membranipora perfragilis MacGillivray, 1895:39. 

 Membranipora crassimarginata var. erecta Busk, 1884:63. 

 Membranipora perfragilis, Wmcks, 1884:278. 

 Amphiblestrum per fragile, Ortmann, 1890 :29. 

 Membranipora serrata, Robertson, 1908:269 (in part). 

 J canthodesia perfragilis, Hastings, 1945:98. 



The zoarium encrusting and rising free into richly convoluted or 

 frilled and variously contorted masses, the frills often anastomosing ; bi- 

 laminar, the layers back to back, but occasionally one layer may extend 

 slightly beyond the other. In the free frills the zooecia are regularly dis- 

 posed, quite regular in form, the lateral walls parallel, the distal wall 

 arcuate; 0.50 to 0.60 mm long by 0.25 to 0.30 mm wide. The zooecia 

 of the encrusting base vary greatly in size and proportions, sometimes 

 being as wide as they are long. The mural rim is finely crenate, the distal 

 as well as the lateral walls. The cryptocyst is distinct, narrow on the sides 

 but continued around the distal end of the opesia ; usually broader at the 

 proximal end, but sometimes limited to the proximal corners. 



There are incipient interzooecial avicularia, smaller than the zooecia, 

 with a spatulate mandible which is without pivot. They appear to be 

 rare and I have found them only on the encrusting base. 



It is recorded as common in Australian waters and is known also 

 from Japan. Robertson (1908:269), under M. serrata, reports of that 



