528 POLYZOA 



A tooth projects from the lower side into the large, subcircular orifice, 

 on each side of which is a small oval avicularium (colony erect or 

 encrusting) . . . Mucronella pavonella 



No tooth : mucro sometimes present . . . .29 



Branches cylindrical. Old zooecia with thick walls. Orifice in 

 young zooecia longer than broad ; beneath it a median pore, 

 29. 1 and in some cases a lateral avicularium with vibraculoid mandible 



Diporula verrucosa 

 A distinct mucro, which may bear an avicularium above Palmicellaria 



Encrusting Cheilostomata. 



Usually growing on a small univalve shell. Orifice longer than 

 broad, indented laterally. Mucro present . . Lepralia edax 



30. -' One or two conspicuous processes, each bearing an avicularium, near 

 the orifice, which is often concealed. Avicularia in many cases 

 found on other parts -of the colony . . Cellepora 



( Zooecia distant ; or in single rows . . . .32 



' \ Zooecia forming continuous expansions . . .36 



_ f An oval aperture, larger than the orifice . .33 



\Noaperture . . . . . .34 



[ A tubular process below the aperture, in some cases : zooecia very 



33. 4 narrow below . . . Eucratea chelata, var. repens 



[ No tubular process below the aperture . Membranipora 



f Peristome much raised below, collar-like . . Phylactella 



' \ Peristome not much raised below . . . .35 



( Zooecia minute, much narrowed below. Orifice small, usually with 

 35. -| a sinus ..... Hippothoa 



^ Zooecia not narrowed below. Orifice with a sinus . Schizoporella 



[Zooecia partly separated by a thin calcareous crust. Colonies 



36.] small ... . .37 



[ Zooecia contiguous . . . . . .38 



( Zooecia pear-shaped. Orifice with a sinus . Hippothoa expansa 

 37. -! Zooecia ovoid. Orifice subcircular, with a tubular peristome 



Lagenipora socialis 



Orifice close to the upper end of the zooecium (unless crowned by an 

 ovicell). Front of the zooecium marked by transverse or 

 radiating furrows or lines. The very young zooecium may 

 possess a membranous area, which becomes roofed in by the 

 union of two lateral series of converging bars (Fig. 257) . 39 

 Characters not as above . . . . .40 



Furrows with uniserial rows of pores (often minute), which are rarely 

 irregular . . . Cribrilina (Fig. 257, A) 



No rows of pores. Distinct transverse lines or spaces and a 

 median longitudinal suture between the bara 



Membraniporella (Fig. 257, B) 



38. 



