302 



the distal wall is provided with an cxj)aiision ending in a thickened, 

 crenulated margin, which partly separates the oa'ciiun IVom the zo- 



cecium Scierodomus n. g. 



(Bil'axaria Busk, p. p.) 

 The peristome is tube-sliaped, projecting, without avicularia, pro- 

 vided with a median opening; in the orecium-bearing zoo'eia there is 



no expansion oi' the distal wall Tessarudoma Norman 



(Porina d'Orb., p. p.) 



S. denticulatus Busk. 

 Bifaxaria denticulata Busk, Challenger, Zoology, Vol. X, Part I, 1884, 



p. 82, PI. XXIV, fig. 3. 

 Bifaxaria denticulata Waters, Challenger, Zoology, Vol. XXXI, Part III, 



1888, p. 15, PI. II, fig. 31. 

 — — Waters, Exped. Antarctic Beige, Bryozoa, 1904, 



p. 59, PI. VIII, figs. 14 a, h. 

 (PI. XIX, figs. 18a-18c, PI. XXII, fig. 14 a). 

 The zooecia indistinctly separated, elongated, thick-walled, strongly arched, 

 increasing evenly in width irom the narrower, proximal end and oblicjuely ascend- 

 ing towards the secondary, terminal aperture, which at a certain age forms almost 

 a right angle with the proximal part of the distal zoan'ium. They consist of an 

 extremely hard and solid, finely striated calcareous mass, which is provided with 

 as a rule fairly densely placed, round or oval, scattered pores leading into long, 

 more or less curved canals. As the colony gradually increases in thickness these 

 pores come to he situated at the bottom of narrow, channel-like concavities, which 

 increase considerably in length with age and give the surface of the colony a 

 characteristic, grooved or longitudinally furrowed appearance. In (juite young zon'- 

 cia the pores may even sometimes be extremely rare in a median belt along the 

 frontal wall. 



I have not been able to determine the form of the primary aperture, nor liave 

 I been al)le to find any operculum. In the youngest, undamaged zoa-cia I have 

 been alilc to find, there is a secondary, more or less regular, broad but low, 

 semicircular aperture, within the proximal margin of which there is a low, but 

 broad, oblicpie tooth-like projection (PI. XXII, fig. 14 a), which on the one side 

 grades into the lateral margin of the aperture and becomes gradually higher 

 towards the other side, where it ends in a rounded, rectangular or obtuse-angled 

 edge not far from llie lateral margin. With the exception of cpiile few zoa>cia, in 

 which an outer, perislomial avicularium is wanting, the peristome in the younger 



