392 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



Key TO THE Genera of Smittinidae 



1. Frontal an olocyst or pleurocyst, sometimes with numerous pores 



but the central area at least imperforate 2 



Frontal a tremocyst with numerous pores over the whole area . 8 



2. With suboral avicularia 3 



No suboral avicularia 6 



3. Avicularia symmetrically developed in the midline 4 



Avicularia asymmetrical, close behind the aperture Rhamphostomella 



4. Avicularian chamber very long, developed from a pore at the 



proximal end of the zooecium Cystisella 



Avicularian chamber short, developed from an areolar pore on each 

 side of the aperture 5 



5. Lyrula and cardelles small or wanting, ovicell imperforate Porella 

 Lyrula and cardelles well developed, ovicell with pores Smittoidea 



6. Avicularia variously situated on the front, never median and sub- 



oral Parasmittina 



Avicularia wanting entirely 7 



7. No lyrula, no umbo Hemicyclopora 



Lyrula well developed, umbo (mucro) usually present Mucronella 



8. No lyrula, proximal border of aperture broadly arcuate, ovicell 



closed by operculum Codonell'tna 



Lyrula well developed, ovicell not closed by the operculum Smittina 



Genus PORELLA Gray, 1848 



The frontal is a thick pleurocyst with areolar pores, otherwise im- 

 perforate (except rarely a few additional pores near the margins) ; a 

 suboral median avicularium which is bilateral in origin with narrow 

 tubules extending around the proximal side of the peristome to the areolar 

 pores; lyrula small, short, often also narrow, wanting in some species; 

 cardelles small and low, often wanting. Ovicell hyperstomial, imper- 

 forate, often becoming completely embedded with later calcification. 

 Genotype, Millepora compressa Sowerby, 1805. 



Most of the species have a smooth frontal, the areolar pores are 

 often occluded in older stages, and the suboral avicularia vary in posi- 

 tion and form, more or less embraced within the "sinus" fold of the 

 peristome or completely proximal to it, the mandible semicircular or 

 pointed in the different species. 



