REPORT ON THE OPHIUROIDEA. 351 



Fig. 2. f . A mouth angle from above, with its massive frames (f) and very large, 

 swollen, peristomial plate (v), jaw (c), socket of first mouth tentacle (;■'). 



,, 3. f. Eadial shield (I) and genital plate (o) in place, with the strong nodular 

 pieces connecting them with the under arm plates (i). Beyond are arm 

 bones in profile. The position of the genital opening is indicated by a 

 dotted line ; genital scale («), side mouth shield (b). 



„ 4. -£. Two joints near base of arm, in profile, dried ; side arm plates (i), bearing 

 tentacle scales (q), and continued upward by a double row of small pieces (j). 

 On the upper surface are the peculiar dorsal spines (z). 



,, 5. {. Skin of one side of an arm joint, flattened and seen from the inside, to show 

 the side arm plate (i) ; the double row of pieces homologous with an upper 

 arm plate (j) ; the dorsal spine (s), and the piece, under the skin, which 

 carries it (/). 



„ 6. {. Lower surface of arm at fifth fork from the tip, to show the Ophiuran-like 

 under arm plate (h), and the side plates (i) bearing tentacle scales (or arm 

 spines). 



,, 7. 3 ^ ) . Upper surface of arm, at fifth fork from the tip, with the last dorsal 

 spines (z). 



,, 8. }. Terminal twigs of the arm nearly in profile, exhibiting the dorsal spines (z), 

 and the elongated, flap-bike side arm plates (i), which bear hooks or club 

 spines (</). 



„ 9. 5 1 °. Three arm joints near end of arm, in profile but somewhat tipped, so as to 

 show the transition from tentacle hooks to the corresponding club spines. 

 On one side there are only hooks (q), supported by elongated side arm . 

 plates (i). On the other, the club spines already are formed ; and these, 

 in turn, gradually take the peg-like shape seen in fig. 6 ; dorsal spine (z). 



,, 10. 1 ?-°. Upper view of a joint from tip of arm (i), the much elongated and partly 

 free side arm plate, bearing terminal hooks (q). There is a superficial granu- 

 lation but no upper plate. 



„ 11. 1 ^°. A similar joint in profile, showing the free side arm plate (i), with its two 

 terminal tentacle hooks (q). 



„ 12. x 5°. Elongated side arm plate (i), and its two hooks (q), from a terminal joint 

 of the arm. 



,, 13. f. Outer face of an arm bone, with its characteristic horizontal hour-glass pro- 

 jection (y). 



„ 14. f. Inner face of an arm bone with its vertical hour-glass projection (/3). 



„ 15. f . Outer face of an arm bone just where the arm forks. The projection (y) is 

 much widened. 



