176 



PROCEEDINGS OF THE ACADEMY OF 



[Jan.. 



Fig. a. S. argutus, operculum 

 mounted in gh^cerine. 



Branchiae too much matted to determine their number. Operculum 

 (fig. a) a thin transparent elongated membranous bulb, flat on top 



and protected by a thin calcareous 

 disk slightly thickened in the center, 

 borne on a long, very slender pe- 

 duncle. 



Thorax with three fascicles of setae 

 and two rows of uncini on each side. 

 All the setae simple tapered blades 

 (fig. b), so small and delicate as not 

 to be clearly seen under a 7 objec- 

 tive, showing no serrations on the 

 edge of the blade even under y"^ oil immersion. Uncini very narrow, 

 hnear, the teeth appearing as but slight roughnesses on the surface, 

 even under the highest power. Abdominal uncini in the first series 

 or segment not appreciably smaller than those on the thorax; setae 

 not found. 



Two specimens on one of the red algae with the following (S. jo-ra- 

 minosus), at Station 3,730. in 34 fathoms, May 16, 1900. 

 Spirorbis foraminosus Bush sp. nov. 



Tube coiled in a similar manner 

 to that of S. argutus, but in the op- 

 posite direction, and larger, with the 

 surface ornamented with three distinct 

 carinae, the middle one the most 

 prominent, the surface on each side, 

 or the interspaces, slightly concave 

 and punctured by minute holes or 

 foramina, apparently caused by the 

 erosion of the thin epidermal layer; 

 the immature forms probably having 

 the entire surface crossed by numer- Fig- b. 

 ous prominent transverse lines. 



Branchiae, the number of which is not determined, are long and folded 

 about, partially covering or protecting the large operculum (figs, c 

 and d), which is in the form of an elongated (apparenth' stiffened b}- 

 a very thin deposit of Hme) cylinder-like broodpouch filled with eggs ; 

 the end protected by a calcareous disk with flaring edge and an inner 

 enlarged basal portion, showing the length of the ventral area attached 

 posteriorly to the secondary calcareous disk on the end of the opercu- 

 lum proper, which is formed of many longitudinal muscles spreading 



S. argutus, seta from 3d 

 thoracic somite. 



