Of 



THE OPIIIUEIDiE. 



113 



§ 



4 



1 



I 



ij 



e» 



■ 



■ 







shields are seen as large ribs. They are long, narrow, widely separated ; 

 their outer third part is naked and smooth, the rest is covered (beneath the 

 skin) w^ith irregular scales, Avhich are firmly united with them, their surface 

 thus being rough. The outer edge of the radial shields is straight, sharply- 

 cut. Some spread scales are found between the radial shields, especially at 

 their outer end. For the rest, only some few small, irregular widely spread 

 scales may be seen in the skin of the disk, and they can only be seen in 

 dried specimens. The ventral side of the disk is covered with rather dis- 

 tinct ovex-lapping scales, which are not enveloped in thick skin. Genital 

 slits very wide and long, reaching almost to the dorsal side of the arm. 

 The genital scale is distinct only towards the margin, grows rather broad as 

 it passes to the dorsal side, where it bears the arm-comb, which consists 

 of short rounded papilla ; about eight to ten are to be seen from above. 

 The genital papilla) short, conical. 



Seven to eight short, equally spaced arm-spines Tentacle pores large in 

 the inner part of the arm, but soon diminishing in size, distinct only to about 

 the middle of the arm. First tentacle pore seemingly opening into the 

 mouth space, but separated therefrom by the outermost mouth papilla. Nu- 

 merous long tentacle scales. First pair of pores has 5-6 on inner (adradial), 

 6-8 on outer (abradial) side; the second has 4 on inner, 6-7 on outer side. 

 They are then gradually reduced in number; on the 9th-10th pore there 

 are no more scales on the inner side ; those on the outer side are reduced 

 to a very small one at about the 20th joint, and this one continues to the 

 end of the arm. 



Among the numerous large specimens but little variation is formd.' At 

 the apex of the jaw there may be some more mouth papilloo, irregularly 

 crowded, so as to resemble tooth papillae, but they are not so really. The 

 secondary arm-comb is often wanting, and often it is only one or two of the 

 first dorsal plates, which are of another shape than the rest. The number 

 of arm-spines varies not a little ; the ty^^ical number is 7-8, but it may 

 be reduced to 5, or raised to 9 or 10. 



In younger specimens (diameter of disk, 13 mm.) there is a rather com- 

 plete covering of plates on the dorsal side of the disk, under the skin, but 

 the scales are very irregular and indistinct in outline ; a central plate is 

 distinct, also five other primary plates, which lie between the inner ends of 

 the radial shields. In still younger specimens presumably the primary 

 plates will be large and cover most of the disk. Only the first dorsal plate 



'|J-r^*^*W-L» -i^Votf'^ "^1 



