514 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



is low and thin but the thickening of the frontal wall gradually sub- 

 merges the operculum. The avicularium is single, in the midline imme- 

 diately above the aperture, about as large as the aperture, rounded or 

 ovate, the mandible semicircular or slightly subtriangular. Occasionally, 

 on Washington and Oregon specimens, there is also a small rounded 

 avicularium placed transversely in the median line below the proximal 

 border of the aperture. 



The ovicell is hyperstomial but is submerged and completely covered 

 by the thick crust of the distal zooecium, visible only in the youngest 

 stages. 



The record of O'Donoghue is in doubt as his description of the 

 avicularia indicates that they are minute and at one side of the midline. 

 Hincks and O'Donoghue have listed the species from a number of 

 localities in British Columbia ; Robertson recorded it from Juneau, Orca 

 and Yakutat, Alaska. 



Albatross Stations: 2886, off the coast of Oregon, the southernmost 

 record, and 3455, off the coast of Washington at 152 fms; also from 

 Puget Sound, Washington, specimens collected by Dr. W. A. Clemens 

 and by Dr. J. L. Mohr. 



Myriozoum subgracile d'Orbigny, 1852 



Plate 64, figs. 3-4 



Myriozoum subgracile d'Orbigny, 1852 ;662. 

 Myriozoum subgracile. Waters, 1900 :69. 

 Myriozoum subgracile, Robertson, 1908 :296. 

 Myriozoian subgracile, O'Donoghue, 1923 :39 :75. 



Zoarial form and general appearance similar to that of M. coarcta- 

 tum. The zooecia are also similar, entirely without separating grooves, 

 and the frontal is a thick tremocyst with large tubular pores. The 

 primary aperture is more elongate than in the other species, the sides 

 straight and converging slightly toward the proximal end which is 

 straight with a deep, narrow u-shaped sinus. The primary peristome 

 is higher than in M. coarctatum, but later covered by the thick frontal 

 wall. The avicularium is single, minute, situated on or near the median 

 line a little distal to the aperture, often wanting, occasionally paired. 



The ovicell, like that of coarctatum, is hyperstomial but is so early 

 embedded in the wall of the distal zooecium that about all that can be 

 seen is a rounded swelling, and even this may soon be obliterated. 



The species is close to M. coarctatum, but the form of the aperture 

 and the minute size of the avicularium easily differentiate it. 



