NO. 2 OSBURN: eastern pacific BRYOZOA — CHEILOSTOMATA 435 



Gystisella bicornis new species 

 Plate 51, figs. (,-1 



Zoarium erect from a small encrusting base, flabellate, reaching a 

 height, in our specimens, of 10 mm, bilaminate. Zooecia moderate in 

 size (0.55 to 0.65 mm long), arranged in quincunx, the frontal smooth 

 with the usual two pores at the proximal end. As in other species of the 

 genus, the frontal is largely covered by the elongate avicularian cham- 

 ber, but the distal end is more erected than in C. saccata and the position 

 of the avicularium is less vertical : the mandible is usually slightly tri- 

 angular or ogival, but is sometimes nearly semicircular, yellow and 

 heavily chitinized and with the tip decurved. On either side of the 

 mandible between it and the corner of the aperture is a short, stout 

 conical process which often projects well above the level of the avicula- 

 rian rostrum; there is much variation in these spinous processes, near 

 the base of the colony they are absent, in younger colonies they are 

 smaller and shorter, in older zoaria they are regularly present except 

 near the base. The primary aperture (seen only at the zoarial edge) is 

 somewhat more than a semicircle, the sides and the proximal border 

 straight; no cardelles and no lyrula; width and length 0.15 to 0.16 mm. 



The ovicell is like that of saccata but smaller, 0.26 mm, round, 

 prominent, smooth and delicately striated when young, but becoming 

 completely embedded with age. 



The species differs from C. saccata in its more erected avicularia, 

 the form of the mandible, the presence of the spinous processes, and in 

 the smaller measurements of the aperture, ovicell and zooecia. 



Type, U. S. Nat. Mus., 11031; paratype, AHF no. 94. 



Type locality: Point Barrow, Alaska, Arctic Research Laboratory, 

 7 to 25 fms. Prof. G. E. MacGinitie, collector, 7 colonies. Also from 

 Orca, Prince William Sound, Alaska, without further data, 3 colonies, 

 and the Dall collection from Alaska, 1 colony. 



Genus MUGRONELLA Hincks, 1880 



Hincks' description indicates merely "Zooecia with a subcircular or 

 semicircular orifice; the peristome elevated in front into a more or less 

 prominent mucro," but later he states "the lower margin of the orifice 

 is almost universally dentate" (that is, with a lyrula). However, the 

 first three species discussed by him are characteristic, and the first men- 

 tioned, Lepralia peachii Johnston (=L. immersa Johnston), is the 

 genotype. 



