303 



zocecia is swollen proximally and divided by an almost rectangular incision (fig. 

 14 a) into two, unequally large halves, the larger of which bears a fairly large 

 avicularium, whilst the smaller is as a rule provided with a rounded swelling 

 provided with some pores. As calcification increases, the incision mentioned en- 

 tirely disappears, the aperture becomes circular and the avicularium comes to be 

 placed deep within this. The very small distal wall, which is provided with ca. 

 7 scattered, uniporous rosette-plates, is in the ooecium-bearing zooecia continued 

 into a plate-like expansion ending in a thickened, crenulated margin (PI. XIX, 

 figs. 18 b, 18 c), and a partial separating wall is thus formed between the ooecium 

 and the zocEcium. 



Avicularia. As above mentioned, an avicularium is placed in the incision on 

 the peristome. It springs from the neighbourhood of the free corner of the. tooth- 

 like projection and its triangular, rounded mandible takes an obliquely distal 

 direction. There is also a second avicularium, which is only seen on grinding 

 down the one half of the zooecium, as it is situated deep down on the inner sur- 

 face of the peristome, almost at a level with the proximal part of the ooecium. 

 The mandible, as also in the second avicularium, is fairly short, triangular and 

 as a rule situated transversely to the longitudinal axis of the zooecium. 



The ocecia, which had already been found by Waters and which occur on 

 numerous zooecia, are for the most part hidden, partly by covering layers and 

 partly by the peristome, and only the proximal part of their frontal wall can be 

 seen more or less deeply withii^ the secondary aperture as a dependent flat part 

 from the distal portion of the latter. This flat dependent part ends in a straight 

 or weakly curved edge and is divided into two lateral areas by a narrow, median 

 belt, which is possibly a calcified portion of the ectoooecium. In sagittal sections 

 they show an elongated, helmet-shaped form (PI. XIX, fig. 18 b). 



The colonies, of which I have examined a number of fragments sent from 

 the British Museum, are free, branched, with the zooecia arranged in 4 alternating 

 rows. The separate branches show as a rule a distinct contrast between a more 

 strongly arched frontal side and a somewhat flatter basal side. Of the 4 zocecial 

 rows two open on the frontal side, whilst the two others have their openings on 

 the margin of the branch, and from the frontal aspect of the branch we can at 

 the same time see three rows of apertures, whilst from the basal aspect we can 

 only see two. 



Challenger St. 320. 



Waters 1 places Piistulipora rastica d'Orb. and Reteporella myriozoides^ in the 



' 115, p. 60—61. 



