224 THE VOYAGE OF H.M.S. CHALLENGER. 



(or distal) face divided by several crests into trapezoidal facettes (mostly three, four, or 

 five). Since the fundamental form of the cylindrical siphosome is bilateral, with 

 symmetrical right and left halves, the paired bracts corresponding in both halves are 

 so symmetrically disposed on both sides of the median plane (or the sagittal plane of 

 the siphosome) that the panelled surface of the carapace offers an elegant and very 

 regular pavement. Their special arrangement on the different sides of the siphosome is 

 intelligible by comparison of figs. 1-3. Since the free terminal facettes on the surface 

 of the scale-carapace are slightly concave, and their edges touch one another, the 

 prominent crests between them form an elegant network over the whole surface. This 

 pavement is in the Pacific Crystallodes mertensii, according to the beautiful figures of 

 Mertens, still more regular and elegant (with subregular rhomboidal meshes, apparently 

 arranged in eight longitudinal columns) than in our Indian Crystallodes vitrea. But 

 also in this latter eight subregular alternating longitudinal columns may be dis- 

 tinguished. The entire cylindrical carapace is very firm and scarcely variable in form, 

 since the protective scales may recede one from another only in a very slight degree. 

 On the ventral side there remain small, free clefts between them, through which the 

 tentacles proceed. Each bract encloses a simple blind canal, which runs in its median 

 line, near to the lower concave surface. 



Siphons (fig. 4, s). — The pedicle of the siphon is rather long and thin, the basigaster 

 rudimentary. The wide cylindrical stomach exhibits eight longitudinal liver-ridges, 

 each of which is composed of a series of conical villi (about ten or twelve large villi in 

 each series). Each villus contains three to five roundish glossy and strongly refracting 

 bodies (probably glandular vacuoles). The proboscis is long and very extensile, 

 cylindrical, with eight strong longitudinal muscle-bands and eight alternating furrows 

 inside. Its distal mouth is armed with cnidocysts and may be expanded as a suctorial disc. 



Tentacles (figs. 1, 5). — The tentacle which arises from the pedicle of each siphon is 

 very long, and bears a series of very numerous tentilla. The pedicle of the latter is 

 also long, and often spirally coiled. It bears a purple cnidoband, which is included 

 in a campanulate involucre and coiled up spirally in three to four turnings (fig. 5). 

 The terminal ampulla (ta) is large, spindle-shaped, and covered with long vibratile cilia. 

 On both sides of its base arise the two paired lateral horns, which are usually curved 

 or spirally coded (fig. 5, tc). 



Palpons. — Each cormidium usually seems to possess four palpons attached to the 

 trunk immediately at the base of the siphon. They are much smaller than the latter, 

 simple, cylindrical, or spindle-shaped tubes, with a thin pellucid wall, very expansive 

 and contractile. Their pointed distal end is closed and armed with a number of cnido- 

 cysts (fig. 4,5). The inner and the outer surfaces are covered with long vibratile cilia. I 

 did not notice and so did not figure the presence of palpacles at the base of the palpons ; 

 but it may be that they were accidentally lost, or that I have overlooked them. 



