78 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



the ooecium and be so completely fused with it as to appear as one struc- 

 ture, or it may be partially separated by a groove. The gymnocyst is well 

 developed and bears a large avicularium ; small lateral avicularia on the 

 mural rim are also present in some of the species. Flustra unicornis 

 Fleming is the genotype. 



Differentiation of the species depends chiefly on the arrangement of 

 the spines and avicularia, which are often of uncertain value but which 

 appear to be fairly constant in this genus. This is especially true of the 

 avicularia; lateral avicularia present or wanting; if present they may be 

 directed forward or backward in different species. The spines are not so 

 constant but erect tubular spines may be present or absent ; other spines 

 may curve closely over the opesia as in arctica, or stand more or less erect, 

 and there is considerable variation in the number present. In the ovicell 

 the transverse rib which is the proximal end of the ectooecium varies so 

 much with calcification that its importance is doubtful, but it serves to 

 differentiate certain species from others which lack the strong rib. 



Key to the Species of Tegella 



1. Small lateral avicularia opposite the operculum 2 



No lateral avicularia 3 



2. A strong, erect, tubular spine, usually on one side only ; one or 



more pointed, curved spines, often wanting armifera 



No erect tubular spines ; 2 to 4 flattened, pointed spines on each 



side bent low over the opesia arctica 



3. Avicularia wanting ; ovicell with a large fenestra or uncalcified 



area at the top magnipora 



Pointed avicularia on the basal gymnocyst, more or less cover- 

 ing the ovicell when this is present 4 



4. No erect tubular spines ; 1 to 3 curved spines bending over the 



opesia, often wanting; ovicell prominent. . . . aquilirostris 

 An erect tubular spine present on one or both sides 5 



5. Ovicell small, deeply immersed, avicularia large. . . robertsonae 

 Ovicell larger and prominent, avicularia smaller. . . . unicornis 



Tegella unicornis (Fleming), 1828 

 Plate 9, fig. 2 



Flustra unicornis Fleming, 1828:536. 

 Membranipora unicornis, Hincks, 1884:7. 

 Tegella unicornis, Osburn, 1923 : 8D. 



Zoarium encrusting. Zooecia moderately large, the opesia large and 

 oval, slightly narrowed at the distal end ; rim broad and finely crenulate, 

 especially on its inner side ; usually bearing 4 spines at the distal end, the 

 more anterior pair small, erect and often wanting, the other pair larger. 



