264 University of California Publications in Zoology. [Vol.4 

 41. Membranipora sandalia Robertson. 



PI. 15, figs. 11, 12, 13, 14. 



Membranipora sandalia Eobertson, 1900, p. 324, pi. 20, figs. 9, 9a, 

 9b; pi. 21, fig. 10. 



Zoarium adherent, thongh rather loosely attached to the sub- 

 stratum, delicate, brittle ; spreading out in a fan-shaped expan- 

 sion, the gelatinous margins often convoluted, and apposed sur- 

 faces often growing together, forming ridges over the colony. 

 ZooBcia, in younger stages oblong, quadrangular, aperture oc- 

 cupying the whole of the front (pi. 15. fig. 11) ; in older stages 

 calcareous ribs extending from the median line to the margin of 

 the lower two-thirds or three-fourths of the zooecial wall (fig. 13) 

 this portion finally becoming covered by a delicate calcareous 

 crust (fig. 14). Aperture, in adult stage (fig. 14, ap.), occupying 

 about one-third or one-half of the front wall. An avicularium, 

 av., with pointed mandible directed right or left on the lower 

 margin of the aperture. Ooeciaf 



Memhranipora sandalia illustrates well the changes that often 

 take place from the early stages of zooecial growth to the adult 

 stage. The zooecia on the margin of a colony possess a mem- 

 branous aperture (fig. 11, ap.) that fills the whole space between 

 the calcareous margins ; at a slightly later stage, calcareous den- 

 ticles (fig. 12, d.) appear on the lateral margins of the lower por- 

 tion of the zooecium and the future aperture, ap., is outlined by a 

 circular rib whose extremities do not quite meet in the median 

 line. At a still later stage (fig. 13) the denticles have grown out 

 forming ribs, rb., extending toM^ard the base of the aperture or 

 toward a median line dividing the basal portion of the zooecial 

 wall into large areolations. The ribs stop rather abruptly at an 

 area, ar., below the aperture on which there forms, in the adult 

 stage (fig. 14), a large, sessile avicularium, while the ribs on the 

 lower portion of the zooecium are almost or completely hidden by 

 a delicate calcareous lamina. In the stage represented by fig. 14, 

 the general aspect of the zocpcia is so different from that of those 

 on the margin of the colony, that they might seem to belong to 

 different species were the transition stages of growth not found. 



Membranipora sandalia has been obtained at Yakutat. Alaska, 

 growing over sponge. 



