ON THREE INTERESTING NEW OEGOl'SIDS FROM THE BAY OF SAGAMI. 145 
seen in each side. The olfactory crest of each side consists of one transverse 
and three longitudinal folds, the latter stretching between the transverse fold 
and the posterior boundary edge of the head. l^ach eye-opening, at the 
middle of the anterior edge, has a distinct sinus, of which the dorsal margin 
is thickened (PI. IV. fig. 8). The siphon tapers a little forwards, and reaches 
the middle of the head ; the collar-like portion of the base is free poste- 
riorly around the viscera except at the nape where it is fi.xed to the skin, 
and the ventral margin is highly arched with a thin membranous border. 
The siphonal resisting cartilages are triangular, with a .spindle-shaped eleva- 
tion in front; the groove is J_-shaped, the longitudinal part curving to- 
wards the ventral side anteriorly. The middle portion of the cartilage is 
joined by the ligament to the mantle cartilage, and the posterior margin is 
also connected at the middle with the same. The dorsal connective ligaments 
of the siphon are in two pairs, one pair of which is median in position and 
the other lateral. The resisting cartilage of the nape is elongate and expand- 
ed anteriorly, with a pair of thick submedian ridges, which extend some 
distance backwards beyond the collar-like portion of the siphon, with ano- 
ther faint longitudinal ridge running between them. 
The arms are subequal, the formula of length being about 2==4=3>i ; 
the longest arm is about one-third the length of the mantle. 
The first and second pairs of arms are about quadrangular in section ; the 
former pair has a narrow web along each proximal half of both outer edges, 
while the latter pair is provided only along the ventral outer edge with a 
web, broader than the preceding ones and extending from the base of the 
arm up to the extreme end. The protective membranes of both sides of the 
first pair, as well as the dorsal membrane of the second pair, are a little nar- 
rower than the length of the suckers ; while the ventral membrane of the 
second pair is slightly broader than the preceding ones, being as broad as the 
length of the suckers. 
The third pair is compressed laterally, being provided along the whole 
median line of the outer surface, with a keel as liigh as tlic thickness of the 
