352 THE VOYAGE OF H.M.S. CHALLENGER. 



Fig. 16. f. Inner fiice of the next bone beyond, already nearly divided, and with a 

 double hour-glass j^rojection {/3). 



„ 17. Astropliyton costosum, Seba, f-. A mouth angle and parts of the interbrachial 

 spaces and under side of an arm, with the skin removed to show the under- 

 lying hard parts. On the outer part of the interbrachial space is a region of 

 naked skin, which is replaced along the arm by large plates, attached to those 

 of the side arm (/). There are no vmder arm plates beyond the first (A) nor 

 are there any tentacle pores, the large holes {i') being only spaces between the 

 plates ; side mouth shields (IS), jaw (c), continuing the mouth frames ; jaw 

 plate (e), tooth papillae {d'). 



„ 18. f. Skeleton of one angle of the disk seen from above, the roof being removed 

 and the radial shields {I) turned up and outwards. The inner jDortion of the 

 interbrachial space is plated ; genital plate (o), genital scale {n), mouth- 

 frame (/), peristomial plate (v), first mouth tentacle (;•'), jaws (c), jaw plate 

 ((?), spine-like tooth {d''). 



,, 19. \*^. Two joints near the tip of a twig, with the double rows of grains and hooks 

 which stand on the thick triangular side arm plates. 



„ 20. •^f*. A joint, near tip of arm, in profile {cf), a tentacle hook (tentacle scale) just 

 formed, and standing on a side arm plate (/'), which also bears a continuation 

 of the double row of grain hooks. 



,, 21. If. (The figure should be turned so that the longer diameter is vertical.) A 

 joint half a dozen forks from the end of the arm. The tentacle hooks have 

 fallen, and the surface is granulated except a part of the side arm plate (i) in 

 front of which is a tentacle pore. 



,, 22. ^^. A joint from a small twig, in profile showing three tentacle hooks {q) 

 standing on a side plate (i) and changing to blunt spines. The surface 

 granulation is a development of that seen in younger stages. 



,, 23. f . Skeleton of a mouth angle seen in profile from the brachial side ; 

 {x), articulating surface to the neighbouring similar angle next which are 

 seen the vertical canals of the radial water tube, and the radial nerve 

 mouth frames (/), peristomial piece {v), sockets for the first and second 

 mouth tentacles {r" and r'), jaw (c), jaw plate (c). 



,, 24. \. Outer face of an arm bone with its horizontal hour-glass projection {y). 



,, 25. |. Inner face of an arm bone with its vertical hour-glass projection (/3). 



,, 26. Gorgonocephalus agassizii, Lym., -f. An arm bone from below, showing the 

 position of the tentacle sockets (r, r). 



