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112 



THE OPIIIURIDiE. 



eacli side^ shorty rounded; rather close set ; the outermost one is wider than 

 the rest, and separates the pore of the mouth tentacle from the mouth space ; 

 that on the apex of the jaw is scarcely longer than the rest. Mouth shield 

 hourglass-shaped ; an obtuse angle within^ outer edge straight, lateral sides 

 deeply restricted by the inner end of the genital slits; the corners rounded. 

 Side mouth shields rather short, almost equally wide in their whole length, 

 meeting within. Mouth angle not prolonged. 



First ventral plate not much smaller than the following ones, polygonal, 



with outer edge strongly curved, inner edge straight. 



The following 



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ventral plates a little broader than long; the second is.longer than the rest, 

 though not so long as broad. Inner and outer edge are strongly curved, the 

 former concave, the latter convex. The lateral sides a little re-enteringly 

 curved through the tentacle pores. The five inner ventral plates are in 

 mutual contact in their whole breadth; from the sixth, the piece in contact 

 becomes rapidly narrower, and from the 8th-9th joint they are wholly 

 separated. Their form then rapidly alters : at first they have an acute angle 

 within, but this soon disappears ; they have then a slightly rounded edge 

 within, whereas the outer side is produced into an angle, with the tip 

 rounded. The plates are thus triangular, with the top turned outward, and 

 lie almost wholly in the base of the next joint, not in that to which they 

 really belong; in this form they continue to the end of the arm. The side 

 arm-plates are flat, straight, outer edge not prominent; on the dorsal side 

 they are separated to the end of the arm. The dorsal plates are four-sided, 

 in the inner part of the arm twice (or more) as broad as long, farther out 

 they gradually become narrower, and towards the end of the arm they are 

 twice as long as broad. They are in contact in their whole width, the inner 

 edge being only inconsiderably narrower than the outer. All the sides are 

 almost straight. The first three dorsal plates are of a somewhat different 

 shape: the first is crescent-shaped, convex within, concave without; the 

 second has inner and outer edge straight, the latter the widest; the third 

 has inner edge straight or slightly concave, outer edge convex; this is the 

 widest of all the dorsal plates. The three described plates are very short ; 

 along their sides is a somewhat elevated line, which bears some small, not 

 very distinct papillse, the secondary arm-comb. Inside these three plates 

 there are yet one or two very small rudimentary dorsal plates. Arms thick 



and round. 



Disk covered with a thick naked skin, through which only the radial 



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