1G2 THE VOYAGE OF H.M.S. CHALLENGER. 



position, and therefore perpendicular to the horizonal main axis of the smaller apical 

 pneumatophore. The truncated apical or upper face, where it unites with the latter 

 (fig. 10), exhibits a short condyle or apical apophysis, is deeply notched, and presents a 

 sort of articular face, into which the solid angle of the apical nectophore, formed by the 

 junction of its two ventral faces, is received. The siphosome (fig. 10, a) enters through 

 the apical apophysis into the hydrcecial canal (m). 



The opposite basal face of the basal nectophore (fig. 9), or the base of the obelisk, is 

 nearly rectangular ; its sagittal diameter is twice as great as its frontal axis. The centre 

 of the dorsal half of the basal face is occupied by the small aperture of the nectosac, 

 which is surrounded by a broad velum (y) and the circular canal, whereas the ventral 

 half of the basal face contains the wide opening of the funnel canal (id) through which 

 the trunk (a) proceeds. The four corners of the basal face are somewhat asymmetrical 

 and project downward as irregular three-sided pyramids ; the two dorsal corners are 

 smaller than the two ventral ; the right dorsal corner (w 3 ) is the smallest, and the right 

 ventral corner (u 1 ) the largest. 



The four lateral faces of the basal nectophore (standing vertically in figs. 1-4) are 

 nearly rectangular, slightly concave, and separated by four prominent, finely serrated 

 edges. The nectosac is seen through the dorsal face (fig. 4, w), the hydrcecial canal with 

 the included siphosome through the ventral face (fig. 3, a). This latter is bisected in 

 the basal half by the hydrcecial fissure ; a broad dentate plate stretching from the right 

 ventral ridge (u l ) over the smaller opposite plate, which arises from the left ventral 

 ridge (u 2 ). These two ventrolateral crests are stronger and project more downwards 

 over the basal face than the two dorso-lateral crests ; the right of these (u 3 ) is some- 

 what larger than the left (m 4 ). The four interraclial crests are not rectilinear, but 

 slightly curved, S-shaped, and turned a little spirally around the vertical main axis. 



The Nectosac of the Basal Necto])hore (figs. 1-4, iv) is slenderly ovate and occupies its 

 dorsal half. It is twice as broad and three times as long as the nectosac of the apical 

 nectophore. The dorsal face is more strongly vaulted than the ventral. The circular 

 basal aperture is small and surrounded by a broad velum (v). The four radial canals of 

 the subumbrella, which discharge into the circular canal, are of unequal length ; the ventral 

 (cv) is shorter, the dorsal (ccl) longer than the two curved lateral canals (ex right, el left). 

 The four canals do not meet in the apex of the nectosac, but a little beyond it on the 

 ventral face ; and from their meeting point arises a rather long peduncular canal, which 

 ascends nearly vertically, pierces the articular apophysis of the upper face of the nectosac, 

 and unites at its apex with the top of the siphosome (figs. 1, 10). 



The Hydrcecial Canal occupies the half of the basal nectophore ; it is rather narrow, 

 subcylindrical, and is separated by a thin jelty-plate from the ventral side of the neigh- 

 bouring nectosac. Its apical opening (fig. 10) is obliquely truncate, ovate, and opens 

 into the apical dorsal part of the apical nectophore (fig. 1). Its basal opening (fig. 9, ui) 



