436 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



The frontal is a pleurocyst, with one row (occasionally 2 or 3) of 

 areolar pores. Spines are present on the oral border. No avicularia. 

 The lyrulae are like those of Smittina, varying in length, breadth, exca- 

 vation of the tip and in the lateral points. Dietellae are present and 

 sometimes characteristic of species. 



Key to Species of Mucronella 



1. Peristome high, tubular, oral spines 8 to 10 major 



Peristome not tubular but forming an umbonate 



process; spines 2 to 6 2 



2. Dietellae long, only two on a side; ovicell with a 



raised lip above the orifice connectens 



Dietellae small and numerous; ovicell without a lip .... 3 



3. Front highly arched transversely; zooecia more elevated 



distally; ovicell high and depressed toward the tip . . labiata 

 Front moderately arched : distal end of zooecium not 



unusually elevated; ovicell broadly rounded . . . ventricosa 



Mucronella ventricosa (Hassall), 1842 

 Plate 52, fig. 3 



Mucronella ventricosa, Hincks, 1880:363. 

 Mucronella ventricosa, Osburn, 1912:243. 

 Mucronella ventricosa, O'Donoghue, 1923:46; 1926:70. 



Zoarium encrusting, usually on shells and stones. Zooecia mode- 

 rately large, averaging about 0.75 mm long by 0.45 mm wide, more or 

 less ovate but varying widely in proportions; very distinct even in full 

 calcification, with deep grooves. The front is ventricose, delicately 

 pebbled with minute tubercles which are usually arranged in radiating 

 lines ; numerous small areolar pores usually in one row but occasionally 

 two. The primary aperture, 0.16 mm wide by 0.13 mm long, is straight 

 on the proximal border, with a moderately broad lyrula. The peristome 

 is thin and little raised on the sides and bears 6 to 8 long erect spines; 

 proximal to the aperture it is raised into a thick fold which usually is 

 continued into a pointed umbonate process overhanging the aperture 

 more or less. 



Ovicell subglobose and prominent, slightly immersed in full calcifi- 

 cation, 0.35 mm wide by 0.30 mm long, imperforate, the secondary cover 

 finely pebbled like the frontal. 



