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



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

 double hour-glass projection (/3). 



„ 17. Astropkyton 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 under arm plates beyond the first (h) nor 

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

 plates ; side mouth shields (b), 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 (1) turned up and outwards. The inner portion of the 

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

 frame (f), peristomial plate (v), first mouth tentacle (■>•'), jaws (c), jaw plate 

 (e), spine-like tooth (d"). 



,, 19. 4 1 °. 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. *£. A joint, near tip of arm, in profile (q), a tentacle hook (tentacle scale) just 

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

 of the double row of grain hooks. 



,, 21. l ] p . (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. 4 j°. 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 ; 

 (.c), 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 /), jaw (c), jaw plate (e). 



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



,, 25. f-. Inner face of an arm bone with its vertical hour-glass projection (ft). 



„ 26. Gorgonocephalus agassizii, Lym., *_-. An arm bone from below, showing the 

 position of the tentacle sockets (r, r). 



