EXPLANATION OF THE PLATES. 



PLATE I. 



Ophiomusium. acuferam, Figs. 1-5. Fig. 1, ^, under surface, showing the mouth-tenta- 

 cles, the curved genital openings, and the two under arm-plates which have tentacles. Fig. 2, f , 

 upper surface, with its peculiar plates and the spines on the back of the arm. In this species and 

 the succeeding one the surface is shown smooth, as it appears under water ; when dry, it is seen 

 to be covered with microscopic points. Fig. 3, f , a portion of the arm, near its tip, from below, 

 showing the complete investment by the side arm-plates. Fig. 4, 2£, the jaws and adjacent 

 parts, from the side: c, the jaws ; e, jaw-plate ; d", teeth; d, mouth-papillae; r, /, the sockets of 

 the second and first pairs of mouth-tentacles. The rudimentary state of the apparatus will be 

 observed : shapeless jaws, small jaw-plate, few and irregular teeth, and the closely soldered 

 mouth-papillse. Fig. 5, %f-, a tentacle of one of the two under arm-plates with its clapper-like 

 scale. 



Ophiomusium testudo, Figs. 6-8. Fig. 6, Jj&, under surface, showing two of the mouth- 

 tentacles, the absence of an under arm-plate on the third joint, and the peculiar marginal disk- 

 plates. Fig. 7, ^-, upper surface, with the intimately soldered plates. Fig. 8, -1^, 3d, 4th, and 

 5th arm-joints, with their two or three minute arm-spines. 



Ophiacantha marsupialis, Figs. 9-10, Y-. Fig. 9, under surface. The arms of a young 

 one protrude from the genital openings. The peculiar shape of the jaws will be observed ; and 

 the unusual size of the first under arm-plate, which completely encloses the second pair of mouth- 

 tentacles. Fig. 10, upper surface. 



Ophioscolex Stimpsonii, Figs. 11-15. Fig. 11, f, under surface. The outlines of some 

 of the parts are dimly seen through the thick skin. Each tentacle has a flap of skin outside it ; 

 and the arm-spines lie along the margin of the arm. Fig. 12, f, upper surface, covered by a 

 thick integument, which is projected over the upper surface of the arms as a transparent film, 

 through which the upper edges of the arm-bones may be seen, and their muscular bundles. 

 Fig. 13, if-, under surface of an arm-joint, with skin removed to show the plates. The small 

 under arm-plate and the side arm-plates are much as in OpMomyxa. Outside each tentacle is 

 its peculiar flap of skin; and, next this, the lowest arm-spines slightly denticulated. Fig. 14, 

 \", upper surface of a joint at tip of arm ; the side arm-plates do not meet above, nor is the 

 vacant space covered by any upper arm-plate. Fig. 15, ±p, the joint from below. Wedged 

 between two side arm-plates is a circular under arm-plate, outside which are the tentacles with 

 their flaps, and the undermost arm-spines. 



