337 



Porella margaritifera Quoy & Gaim. 

 Flustra margaritifera Quoy & Gaimard, Voyage de I'Uranie, Zoologie, p. 606, 



Pi. 92, figs. 7, 8. 

 Lepralia margaritifera Busk, Catalogue of Marine Polyzoa, Cheilostomata, p. 72, 



PI. CI, figs. 5, 6. 

 Flustra margaritifera Jullien, Mission du Cap Horn, Bryozoaires, 1888, p. 58, 



PI. 9, fig. 1. 

 Lepralia margaritifera Waters, Challenger, Zoology, Vol. XXXI, III, 1889, p. 26, 



PI. Ill, figs. 15, 16. 

 (PI. XVIII, Hg. 8 a). 

 The zooecia elongated, hexagonally lyre-shaped, strongly arched and provided 

 with a circle of marginal pores. These soon come to lie in areas, bounded by 

 ribs, which radiate in from the margin to the suboral avicularium; and with 

 the continued deposition of the calcareous substance these areas are at length 

 transformed to pear-shaped pits. The aperture has a semicircular anter, and we 

 can distinguish in this between a straight or slightly convex, median part and 

 two short, curved, distally diverging lateral parts. Small distinct hinge-teeth. 

 The operculum, which is not separated from the compensation-sac, is weakly 

 chitinized and provided on each side with a chitinous ridge, which is slightly 

 angularly bent and its proximal portion is in the greater part of its length far 

 removed from the margin. The strongly curved or angularly bent distal wall is 

 provided on each side with a row or zigzag belt of small, uniporous rosette-plates, 

 and the distal part of each lateral wall has one multiporous rosette-plate. 



The ooBcia, which on the colonies examined occur on the majority of the 

 zooecia, seem only to consist of a single, independent calcareous layer and have 

 therefore probably .been covered by a membranous ectoooecium. They are ori- 

 ginally furnished with fine radiating striae, but in older zooecia they show con- 

 centric thickenings arising from the covering calcareous layer. 



Avicularia. The suboral avicularium, which has a broad, triangularly rounded 

 mandible and a broad, sac-like chamber, does not attain quite a third of the 

 whole length of the zooecium. In the older zooecia it shows like the ooecium con- 

 centric thickenings. In one of the small colonies examined a number of zooecia 

 are provided immediately distally to the ooecium on the one side with an avi- 

 cularium somewhat variable in size, which is of an irregular elliptic form, as it 

 increases in breadth towards the distal part of the opercular area, and this espec- 

 ially in the larger avicularia is provided with a well-developed cryptocyst. In 

 the younger zooecia these avicularia, the mandible of which is as a rule directed 



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