PROF. OWEN ON NEW AND RAEE CEPHALOPODA. 157 



between a pair of suckers, taken at the basal attachment of their peduncles, is 2 inches, 

 where they are widest apart. The greatest width of the acetabuliferous tract within 

 the marginal folds is 3^ inches. 



The section of the basal part of the arm shows the muscular mass to be divided by a 

 thin aponeurosis (PI. XXXV. fig. 1, d) into a peripheral {e) and a central (/) portion. 

 The peripheral muscular mass, e, at the inner side, a, shows a thickness of 6 lines ; 

 it is traversed by the main artery of the arm, g. This part of the peripheral mass 

 gradually diminishes on each side to a thickness of 2 lines, and then as gradually 

 increases to 4 lines at e' ; when, bending in to the outer side of the arm, it thins off to 

 half a line, the aponeurotic boundary coming there almost into contact with the outer 

 integument. The transverse diameter of the inner muscular mass at the dorsal third 

 is 2 inches 8 lines ; at the ventral third it is 2 inches : and here the section shows the 

 nerve, h, in a canal of 5 lines diameter, the nerve being surrounded by loose cellular 

 tissue including venous channels. 



The cups gradually increase in size to the sixth or eighth, which has a diameter of 

 three fourths of an inch ; and here the acetabuliferous tract and its marginal folds 

 show the dimensions given in fig. 2, PI. XXXV. They begin very gradually to diminish 

 beyond the basal ten or twelve inches of the arm. 



Of the large cups the peduncle is 7 to 8 millims. in length ; its base is 5 millims. in 

 breadth, and gradually contracts to 2 millims. before insertion. This is at the side of 

 the base of the cup, where the cup is least deep ; and here there is a depression for 

 receiving the peduncle (PL XXXV. fig. 3). 



The base of the cup is 20 millims. in diameter ; it is slightly convex, shows a fleshy 

 tint, which changes to a white aponeurotic appearance at the periphery ; and this 

 character of the exterior of the cup continues to the aperture, which is circular and 

 10 millims. in diameter. From this aperture slightly projects the margin of the broad 

 chitinous hoop lining the walls of the cavity. The bottom of the cup, 12 millims. in 

 diameter, is soft, muscular, covered by a thin, transparent aponeurosis, and seems, by 

 its size, to have been capable of assuming the shape requisite to act as a kind of piston, 

 and by the vacuum so produced to cause outward pressure to aid in infixing the teeth 

 of the denticulate free border into the surface to which the arm may have been applied. 



The suckers, as they extend along the arm, diminish in diameter in a greater degree 

 than in depth, and the smaller acetabula make a nearer approach to the spheroid form 

 (PI. XXXIV. fig. 2); but each hangs by a proportionately long peduncle until they come 

 to near the end of the series, where they show but 1 millim. diameter, passing out 

 of sight at about 2 inches from the pointed termination of the there gradually attenu- 

 ated arm. The basal cups of the same side or series occur at first at intervals of 24 

 millims. ; and as the longitudinal interval shortens, the transverse one increases to an 

 extreme of 2 inches, then progressively diminishes with the diminishing size of the arm. 



The integument of the acetabuliferous tract shows a denser surface and paler tint 



2c2 



