146 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



semielliptical or crescentric, perforated by very small tremopores, 

 surrounded by a special thick and granulated mural rim; the opesium 

 is semielliptical, transverse, large; it contains a vestibular arch. 

 The opesiular indentations are large, round, symmetrically arranged 

 on each side of a salient lip attached to the proximal mural rim of 

 the cryptocyst. The polypide tube is buried behind the salient lip 

 (and visible only in elevating the preparation). The avicularium 

 is primoserial, large, triangular, without pivot, with an oval opesium; 

 the mandible is small, ungulate, The superior sclerite of the opercu- 

 lum bears four hooks. The number of hooks to the mandibular 

 operculum is variable for we have noted 4 to 6 and there are 8 on 



A C 



Fig. 36. — Steganoporella mandibulata Harmer, 1926 



A. Large operculum, X85. B. Avicularium mandible, X85. C. Small 

 operculum, X85. 



Harmer's figure. The details of this operculum are shown on Har- 



mer's figure. 



Measurements. — 



„ . \Jio = 0.35mm. n \Lz = 0.90-1.10 mm. 



Opesium L _ A Zooecium 7 _ 



r Uo = 0.50mm. [lz= 0.60-0.75 mm. 



. . , . f Lav = 0.45 mm 

 Aviculanumi-, _„_ 



Hav = 0.35 mm. 



Structure. — We have had the chance to study living specimens. All 

 of the details of the zooecia are covered over by a thick opaque 

 ectocyst; the articulation of the opercula is a line somewhat concave 

 attached laterally to the two inferior extremities of the distal dome. 

 The ectocyst entirely covers the avicularium and it contains only a 

 small perforation corresponding to the mandible. 



There is only one form of zooecia. In spite of the presence of the 

 primoserial avicularia this species is indeed a Steganoporella ; its 

 opesium contains the characteristic polypide tube; its operculum is 

 provided with a sclerite with a prong as in most other species of this 

 genus. 



Biology. — The species prefers depths from 30 to 40 meters but can 

 descend to a greater depth. The larvae became fixed toward the end 

 of the month of February, 1909. The species accompanies Stegano- 

 porella magnilabris but it is much more uncommon. 



