[85] CEPHALOPODS OF NORTHEASTERN COAST OF AMERICA 295 



diameter placed transversely and somewhat obliquely, while the narrow 

 and deep sinus extends forward and somewhat downward. When partly 

 closed (Plate XIX, fig. 4) the opening between the lids generally be- 

 comes more oblong, and sometimes approaches a triangular form. 



The mantle is thick and very muscular ; its anterior margin has a con- 

 cave outline beneath, forming a slightly prominent angle on each side ; 

 from these angles it advances somewhat to the slight median dorsal 

 angle, which projects forward but little, and does not form a distinct 

 lobe, and sometimes it is hardly noticeable, even as an angle, the trans- 

 verse outline of the edge on the dorsal side being, in that case, nearly 

 straight, or advancing a very little in the middle. 



The sessile arms are rather stout, tapering to acute tips. The dorsal 

 arms are a little smaller and shorter than the others ; the second and 

 third pairs are nearly equal in size and length, the second often a trifle 

 the longer ; those of the fourth pair are usually intermediate in length 

 between the first and second pairs. 



All the sessile arms are stout and armed with similar suckers. Along 

 their inner angles, outside the suckers, they are all similarly provided 

 with marginal membranes, which rise to about the same height as the 

 suckers, on each side. Just proximal to each sucker, ou the inner face 

 of the arm, arises a thickened, transverse, muscular fold, that extends to 

 the edge of the lateral membrane, which often recedes between their 

 extremities, so as to have a scalloped outline. 



The dorsal arms are a little shorter and decidedly smaller than the 

 others. The two lateral pairs of arms are stoutest and longest, and 

 nearly equal, sometimes one pair and sometimes the other being longest. 

 The ventral arms are a little longer than the dorsal and shorter than 

 the lateral ones. The dorsal and upper lateral arms are trapezoidal in 

 section, with the inner face rather broad. The dorsal arms have a 

 slightly elevated, median dorsal crest, commencing near the base and 

 running to the tip. Those of the second pair have a broader, mem- 

 branous fold on the lower outer angle, along the whole length. Those 

 of the third pair are stouter than the others, and much compressed lat- 

 erally, with the outer surface rounded, close to the base, but becoming 

 compressed and keeled farther out, and having a high median ridge 

 or crest along its middle region, becoming narrow toward the tip. The 

 ventral arms are trapezoidal in section, with a narrow fold along the 

 outer angle, which is acute, while the inner ventral angle is rounded. 



The tentacular arms (Plate XVIII, figs. 1 <?, 2) are long ; when extended, 

 in fresh specimens, they reach back beyond the base of the caudal fin. 

 They are rather stout, rounded-trapezoidal along the peduncular portion ; 

 along the upper-outer angle a thin fold runs from the base to the tip, 

 becoming on the back side of the club a wide carina, which often folds 

 down obliquely toward the upper margin of the club; two less marked 

 folds run along the inner angles, defining a narrow inner face along the 

 whole length, but on this face there are no suckers, except close to where 



