300 



ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



long by 0.35 mm wide ; the frontal area nearly flat, with a row of large 

 areolar pores separated by short costae, without other decoration. The 

 aperture is very large and quite variable in size, usually about 0.30 mm 

 wide by 0.25 mm long, rounded, but somewhat straighter on the proxi- 

 mal border; peristome low and thin (often scarcely visible) except on 

 the proximal border where it projects forward as a short, broad mucro, 

 very variable in size and form. No oral spines, no cardelles. On either 

 side of the aperture is an oval avicularium, very slightly elevated and 

 with the short-spatulate mandible directed forward. No ovicell. 



Widely distributed in the Arctic Ocean, southward along the Atlantic 

 coast to Cape Cod, Massachusetts, and on the Pacific coast to Puget 

 Sound. 



Not taken in the Hancock dredgings, but represented in the col- 

 lections by specimens from San Juan Island, Friday Harbor, Puget 

 Sound ; U. S. Alaska Crab Investigation, Alaska, Sta. 20-40 and 24-40 ; 

 Punuk Island, Bering Sea (no further data) : and Point Barrow, 

 Alaska, G. E. MacGinitie, collector, Arctic Research Laboratory. 



Umbonula alvareziana (d'Orbigny), 1847 

 Plate 36, figs. 4-5 



Escharina alvareziana d'Orbigny, 1847:44. 

 Lepralia alata Busk, 1854: 71. 

 Alucronella alvareziana, Jullien, 1881 :5. 

 Smittia alvareziana. Waters, 1905:239. 



Zoarium encrusting a shell, white and unilaminar. Zooecia small 

 for this genus, 0.40 to 0.55 mm long by 0.30 to 0.40 mm wide, ovate 

 or elongate-hexagonal, distinct. The frontal is a thick pleurocyst, con- 

 siderably arched, with a row of large areolar pores between which are 

 prominent ribs running toward the center of the front ; a broad rounded 

 umbonate process near the aperture. The primary aperture is nearly 

 round, somewhat straighter on the proximal border, length 0.11, width 

 0.12 mm. The operculum is moderately thin, faintly yellowish, with a 

 slender sclerite on each side which originates at the point of attachment 

 and curves inward to the muscular attachment which is well separated 

 from the thin border. No lyrula, no cardelles; 4 minute spine bases are 

 present on some of the marginal zooecia. The primary peristome is 

 scarcely evident but the thick frontal submerges the operculum below 

 a wall which extends proximally to the umbo. A small avicularium with 

 an acute mandible is often present, usually on the side at the widest 

 part of the zooecium, with the rostrum directed laterally. 



