20 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



the erect and the encrusting stages. The spinules margining the inner 

 edge of the cryptocyst are variable in the extreme; rarely seen in 

 membranacea ; in other species there may be a few small ones, a few- 

 larger ones, or they may be numerous along the sides to the level of 

 the operculum; sometimes they fringe the edge of a broad crypto- 

 cystal shelf. 

 5. The generic description of Acanthodesia indicates only two differential 

 characters, the proximal dentate tooth and the lateral cryptocystal 

 spinules, both of which are frequently wanting on the erect stage and 

 especially on the encrusting stage of the genotype A. savarti. Further- 

 more the erect character of savarti cannot be considered of much 

 importance since the zoarium is often broadly encrusting and some 

 other species which have been placed under Acanthodesia may rarely 

 develop bilaminate folds or frills. 



As a result of the above analysis I feel obliged to return the species 

 of Acanthodesia to Membranipora. It is a question of retaining Mem- 

 branipora for the whole series or of placing them all under Acanthodesia^ 

 unless some more positive differential character can be determined. As 

 Membranipora appears to be properly established, Acanthodesia must go 

 into synonymy. 



Key to Species of Membranipora 



1. Cryptocyst narrow or wanting 2 



Cryptocyst better developed, usually extending forward around 



the aperture 5 



2. Cryptocyst wanting, rarely a trace; tubular distal short spin- 



ous processes membranacea 



Cryptocyst present forming a narrow shelf 3 



3. Cryptocyst smooth ; no tubercles ; thick brownish ectocyst . pachytheca 

 Edges of cryptocyst serrate 4 



4. Frontal membrane with chitinous spinules; distal spines long, 



acute, the bases often calcified villosa 



Only the distal spines present, short and tubular . . serrilamella 



5. Distal tubercles heavily calcified, often fused across the middle, 



sometimes spine-like tuberculata 



Tubercles, if present, low rounded knobs 6 



6. A flat shelf extends inward from the edge of the descending 



cryptocyst 7 



The descending cryptocyst only, with a few spinules 8 



7. Cryptocyst very broad and evenly developed on the sides, with 



long, evenly distributed spinules hastingsae 



Cryptocyst broad proximally, very irregular, with spinules of 



various sizes and forms tenuis 



