310 A. E. Verrill — North American Cephalopods. 
forward as the posterior border of the eye, or even beyond it. Dorsal 
connective cartilage long, tapering backwards, with a very prom- 
inent, broad, dorsal keel; the anterior end is free and shaped like 
the end of the pen. Siphon large, rounded anteriorly, with a broad, 
bilabiate opening; lateral cartilages (PI. XL, fig. 1 , /*) long and 
narrow, subacute anteriorly, posterior end with a thin, rounded, 
outer lobe ; median groove narrow. The connective cartilages of the 
mantle (fig. 1,./*) are simple, longitudinal ridges, fading out grad- 
uallv posteriorly. Head moderately large, usually narrower than 
the mantle ; smaller in the male than in the female ; eyes large ; 
nuchal crests (fig. 1, oh) above the ear, formed by longer upper, and 
shorter inferior, oblique, longitudinal membranes, the two united by 
a doubly curved, or V-shaped membrane, having its angle directed 
forward, the whole having a rude, W-sbaped form. 
Arms large, stout, the three upper pairs successively longer ; the 
veutral ones a little shorter than the third pair, and a little longer 
than the second pair. All the arms have narrow, thin, marginal 
membranes, strengthened by strong, transverse, muscular ridges. 
The first and second pairs of arms are trapezoidal at base ; third pair 
stouter, compressed, with a keel on the middle of the outer side. 
Suckers in two regular rows on all the arms, deep, very oblique ; 
largest on the lateral arms ; those on the ventral arms are smaller, 
but otherwise similar. Horny rings yellowish, or brownish (white 
when fresh), strong; on the larger proximal suckers the outer or 
higher side is divided into about six broad, flattened, incurved teeth, 
which are blunt, subtruncate, and sometimes even emarginate at tip, 
remainder of margin nearly even ; the smaller suckers, toward the 
tips of the arms, have the teeth longer, much more slender, and more 
acute. 
The tentacular arm (PI. XXIX, fig. 2) with fresh specimens, in full 
extension, may reach back nearly to the end of the body ; with pre- 
served specimens it seldom extends beyond the middle of the caudal 
fin ; it is rather slender, compressed, and has a narrow, thin, mem- 
branous keel along the outer edge, which becomes wider at the club ; 
on the distal half of the club it is much wider and runs a little 
obliquely along the back part of the upper side, where it is usually 
folded down against the side, its inner surface being whitish. The 
club is rather broad and thick, with a wide, scalloped, marginal 
membrane along each edge ; these membranes are strengthened by 
transverse muscular ridges, which commence between the large cen- 
tral suckers and fork at the pedicels of the marginal ones. Along 
