152 LOWER INVEliTEBRATES. 



powerful muscular action called for in the i-ajjid whip-like motion of the arm. 0. 

 lineata occurs in Florida, and three or four species are found in southern and Lower 

 California. OjMociasina uttenuatmn is a curious form found in the South Atlantic. 

 The examples taken had six arms, the disc is covered with thick soft skin, and the 

 arms, which are very long and slender, ha\e the lower and side ])lates imjjerfectly 

 calcified, and no u]>per plates. The sjnnes are short, three on each joint. The two 

 known species of Ophiohehi,s are remarkable for the curious minute spines or pedicel- 

 larise, having the form of a long-handled jiarasol, that take the place of the ti-iie ai-m- 

 spines on the outer ann-joints. One of the most singular of ophiurans is Ophiothelia 

 supplicans., in which the disc is sha]ied like a high sugar-loaf, and the arms can be raised 

 u])wards. The arms bear u])on all the joints beyond the ninth a cluster of three or 

 four minute jiarasol-like pedicellariae, set a little inside the true arm-spines, which con- 

 tinue to the end of the arm. The under surface of the disc is curiously ornamented. 

 A frill of long, flat, curved ]ia])ilhe is st't upon each mouth-angle, which, ending in- 

 wardly in a shar]i tooth, resemble so many birds' heads with a pointed bill. Externally 

 to the mouth pajiillae are three ])arallel rows of regular club-shaped flat papillae. This 

 form is only known from south-west of Juan Fernandez, and was taken at a depth of 

 (ine thousand eight hundred and twenty-five fathoms. Ophj/omijces has a very pecu- 

 liar arrangement of mouth ])apillae, and two of its species occur between five hundred 

 and one thousand fathoms. 



Two or three genera of (Jj)hiuritla' contain species with cylindrical arms, while the 

 entire animal is clothed with a thick skin, and the arm-j)late8 are imperfectly developed. 

 They thus a])proach the Astro])hytidic. In Opiliiohi/rsit rudis, which was taken 

 off the entrance to Port Phili]), in tliirtj-eight fathoms, each ;n-m is about twelve 

 inches long, though the disc measures only about an inch. 



Ophio»n/Mi t'ivipara is, as the name implies, a ^-i^■iparous species. 



The best known genus of .Vstropiiytid.h; is Astrophijton itself, of which seven 

 species are known. Though there are no arm-s])ines, the outer branches of the arms 

 have s])ine-like tentacle scales. The long bar-like radial shields of the disc are covered 

 by the thick skin, but show as elevated radiating ribs reaching to its centre. Under 

 the skin of the ;n-ms there ai'e side arm-]ilates, which co^er the lower side of the arms, 

 but there is only a basal under arm-j)late, and there are no upper arm-plates at all. 

 Gorgouocephalus has also branching arms, but the )>lateN under the skin of the disc 

 are differently arranged, and the arms, wide at their base in Astrophyton, are here 

 narrow, while the forkings are less numerous than in that genus. The young has at 

 first a flat disc covered with jilates like that of an ordinary ophiuran, this first becomes 

 covered a close granulation ; then both the granulation and the disc-})lates atrophy, 

 excejrt those of the margin, which continue to grow and multiply ; and finally the 

 radial shields acquire their great length and height. In Euryale no ])roper arm-spines 

 are ])]-esent, and in Astroclon and Trichaster the forks are but few. The total length 

 of an arm of T. propuynatoru is about sixteen inches. Among the Astrophytidte with 

 unbranched arms the principal genus is A»trochet)ifu which has well-formed under arm- 

 plates like an ophiuran. Ophiocreas uhi/SKk-oht Avas taken in twenty-three hundi'ed 

 fathoms. 



Obdek II. — ASTEROIDEA. 



The differences which distinguish the star-fishes from the ophiuroids are scarcely 

 less important than those which separate either from the sea-urchins, yet the external 



