434 PROCEEDINGS OF THE ACADEMY OF [July, 



shaped fold of membrane embracing between its arms a series of 

 8-10 shorter and more fleshy longitudinal folds. 



Arms moderate, squarish, fairly attenuate, averaging about half 

 as long as the mantle; unequal, the order of length almost always 

 2, 3, 1, 4, although there are occasionally slight variations from this 

 formula. Umbrella lacking, but the outer angles of all the arms 

 equipped with a firm fleshy keel especially developed on the basal 

 half of the third pair, and a delicate trabeculated swimming mem- 

 brane, which is least evident on the ventral arms and widest on the ven- 

 tral margin of the third pair. Suckers decidedly small (PI. VI, fig. 4) ; 

 rather distantly placed at the base in two regularly alternating rows, 

 becoming more crowded at the tip ; the interspacing between the rows 

 very variable, apparently dependent mainly upon the degree of 

 compression of the arms; suckers of the lateral arms slightly, but 

 not at all conspicuously larger than those of the dorsal and ventral 

 pairs ; on an arm of the second pair some 56 to 60 suckers can readily 

 be counted without using a lens. Horny rings well developed, 

 their lower margins ordinarily smooth, but with 9 to 12 stout acute 

 teeth, accompanied by occasional intervening denticles on the upper 

 edge; these teeth are largest at the apex, but the median one is not 

 particularly differentiated in this respect more than its neighbors. 



Tentacles stout, moderate; the club slightly expanded, its sucker- 

 bearing portion including about 60-65% of the total length in the 

 adult (55-71%, according to Pfeffer); in general structure entirely 

 similar to 0. hawaiiensis, 15 the horny rings of the large median 

 suckers armed with about 17 rather short, stout, acute, subequal 

 teeth, occurring in regular alternation with an equal number of very 

 low squarish plates, both teeth and plates being more regular, though 

 somewhat more weakly developed than in 0. hawaiiensis. A small 

 sucker of the marginal rows shows about 18 acute teeth, larger and 

 longer on the upper margin where they are accompanied by a few 

 alternating denticles. 



In young specimens, such as No. 273, the body appears more 

 slender and the fins much shorter, both in proportion to the mantle 

 length and their own width. 



The chief measurements of eight specimens are given in the 

 following table : 



15 Ommastrephes hawaiiensis new species: A Hawaiian form closely allied 

 to O. sloanii (i.e., pacificus), but with much larger and fewer suckers on the 

 sessile arms of the adult and with the central upper tooth of the horny rings 

 distinctly larger than any of the others. 



