EXPLANATION OF THE PLATES. , 33 



acters here to be seen which separate it from Aiiip/iiura. The small tentacles are somewhat 

 protruding, each with its two scales. Fig. 30, upper surface, showing the strong, coarse scaling 

 and thick upper arm-plates of the genus. Fig. 31, arm-spines. 



PLATE IV. 



Astrophyton Pourtalesii, Figs. 41-43. Fig. 41, |, under surface of the interbrachial 

 space which has the maJreporic l)ody. On the mouth-angle are the few and small tooth-spines, 

 and the mouth-tentacles. Following the arm, the first joint has tentacles with no spine ; the 

 joints beyond have, for the most part, three or four spines to each tentacle. The narrowness of 

 the arm and the single fork within the disk will be noted as compared with the broad arm and 

 three forks of Fig. 44. Fig. 42, \, upper surface, showing the low radial ribs, sparse granula- 

 tion, and smooth arms. Fig. 43, W a joint at the tip of the arm, showing the peculiar minute 

 spines, which are folded down, more or less covered by skin, and placed in two alternating rows. 

 Below are the large tentacles {(/), and their hooked spines (q), cased in skin, of which there are 

 two to each pore on this part of the arm. The northern species, A. Af/asshii, has also two large 

 tentacle-spines to each pore at the tip of the arm (Figs. 49, 50, q, q'), with a ridge correspond- 

 ing. In Fig. 50, a tentacle may be seen pi-otruding from several of the pores. 



Astrophyton spinosum, Figs. 44 - 47. Fig. 44, \, under surface, with one of the five 

 madreporic shields. At the mouth-angle is a crowded clump of numerous tooth-spines, and, on 

 either side, a mouth-tentacle ; just outside is a double swelling, which is a part of the jaws. 

 There are no tentacle-spines on the broad arms, and the pores are represented only by feeble 

 depressions. Fig. 45, |, upper surface, with the wide high radial ribs, and the broad cicatrices 

 at their outer ends. On the disk and arms are the characteristic groups of small spines. Fig. 

 46, -"y", a joint from tip of arm. Each ridge has a double row of granules bearing minute hooks ; 

 and each depression has also a double row of granules, which have not so much of a pit in their 

 centre as is represented in the drawing. A joint of similar chaiucter is that of A. cacaoticum, 

 Fig. 51, where the specimen was dried and many of the booklets rubbed off, showing the gran- 

 ules on which they stood. It must be borne in mind that these granules do not correspond to 

 side arm-plates, nor their booklets to arm-spines. Where booklets are found among Ophiuridre 

 they are arm-spines and stand on side arm-plates, as may be seen in the young of Ophiothe/a 

 isidicola, Fig. 60, where an arm-spine (p) and booklets {p') are found on the side arm-plate (i). 

 Fig. 47, f, upper surface of arm, near the disk, to show the granidation, and the row of small 

 spines which crowns each joint. 



Astrophyton exiguum, Fig. 48, f . Upper surface, from the original and unique specimen 

 of Lamarck in the (!arden of Plants. The specimen has the granulation partly rubbed off, ex- 

 posing the compound radial shields or ribs (1) which characterize the genus. It doubtless is a 

 young one, which adds to the trouble of finding what the species really is. 



Astrophyton Agassizii, Figs, 49, 50. Tip of arm. from a living specimen, much magni- 

 fied : side, and under surface. 



Astrophyton cacaoticum, Fig. 51. Joint from tip of arm, dried, and much magnified. 



Astrotoma Agassizii, Figs. 52-50. Fig. 52, \, disk and one arm complete, from above. 

 Fig 53, y, under surface, showing the finer and coarser granulation, the Astrophytou-like tooth- 



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