270 A. E. Verrill — N'orth American Cephalopods. 



when more open the aperture is still usually somewhat angular; the 

 anterior sinus is narrow and extends downward and forward. 



The eye-lids form, when nearly expanded, an iiTegular oval, the 

 longest diameter placed transversely and somewhat obliquely, while 

 the narrow and deep sinus extends forward and somewhat downward. 

 When partly closed (Plate XXIX, fig, 5) the opening between the 

 lids generally becomes more oblong and sometimes approaches a 

 triangular form. 



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

 concave 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 fonn a 

 distinct lobe, and sometimes it is hardly noticeable, even as an angle, 

 the transverse 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 inter- 

 mediate 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 on 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 scolloped 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 fold, commencing near 

 the base and running to the tip. Those of the second pair have a 

 broader, membranous fold on the lower-outer angle, along the whole 

 length. Those of the third pair are stoiiter than the others, and much 

 compressed laterally, with the outer surface rounded, close to the base, 

 but becoming compressed and keeled farther out, and having a high 

 median ridge along its middle region, becoming narrow toward the 

 tip. The ventral arms are trapezoidal in section, with a narrow fold 



