132 OPHIUROIDEA. 



The oral opening is surrounded by five re-entrant angles, which correspond to the 

 intervals of the five arms ; from the peristome proceed five buccal fissures, in a line 

 with the axis of the arms ; their borders are in general covered with a series of papiUae 

 or plates, and they terminate in a cone of calcareous pieces which perform the part of a 

 jaw. PI. XIII, figs. 1, 3, 4, 5, 6, show various forms of these dental instruments. At 

 the extremity of each fissure a series of osselets, occupying the interior of the arms, take 

 their origin ; their under surface is grooved for lodging a vessel, and between their lateral 

 expansions spaces are formed to receive the base of the fleshy tentacules near the disk. 



HISTORY. 



The older naturalists united the Ophiurid^ to the Asteriad^. Linck^ first described 

 certain species under the common name Stella marina, and designated two species, 

 8. laceriosa, and S. longicauda, to express the resemblance their arms had to the tail of a 

 lizard ; another species, provided with long spines proceeding from the lateral parts of the 

 arms, he called Bosnia scolopendroides^ from the resemblance of the rays to the body of 

 a Scolopendra. The Ophiuroidea with ramified arms, as the AsterophydicB, were distin- 

 guished by Linck from the simple-rayed forms under the name Astrophyton. Seba^ 

 figured many Ophiuree among the Star-fishes. Pennant^ in his ' British Zoology,' and 

 O. F. Miiller* in his ' Zoologia Danica,' have described many in the genus Asterias ; and 

 it is under this generic name that all the species of Ophiurida and Asterophydia known 

 to Linne^ were described, in the thirteenth edition of the ' Systema Naturae,' by Gmelin. 

 Lamarck," in his ' Systeme des Animaux sans Vertebres,' 1801, and in his larger work on 

 the same subject, 1816, established the genera Ophiura and Euryale, taking Asterias 

 ophiura, Miill., as the type of the first, and Astrophyton scutatum, Linck, for that of the 

 other. These generic distinctions, first made by Lamarck, were preserved by Delle Chiaje,''' 

 Risso,® and De Blainville -^ it was not until Professor Agassiz's ' Prodrome'^" appeared 

 that new generic subdivisions of the order were proposed ; in this essay the Ophiurida 

 were thus defined and classified. 



The Ophturid^ differ from the Asteriadae in this, that the central part of the body 



1 Linck, ' De Stellis Marinis,' fol., 42 plates. Lypsise, 1733. 



2 Seba, ' Locupletissimi Rerum Naturalium, &c.,' 3 vols, folio, pi. x — xv, 1734. 

 ^ Pennant, 'British Zoology,' vol. iv, p. 60, 1776. 



* 0. F. Miiller, 'Zoologia Danica,' 2 vols, folio. Lips., 1779—1784. 



^ Linn^, ' Systema Naturae,' ed. 13, par Gmelin. 1789. 



^ Lamarck, 'Systeme des Animaux sans Vertebris,' 1 vol. 8vo. Paris, 1801. 



7 Delle Chiaje, ' Memorie suUa storia e notomia,' &c. Napoli, 1825. 



8 Risso, ' Hist. Naturelle de I'Europe Merid.,' 5 vols. Paris, 1826. 



^ De Blainville, ' Manuel d'Actinologie,' 1 vol. 8vo, plates. Paris, 1834. 



10 Agassiz, 'Mem. Soc. So. Nat. Neuchatel,' vol. i, p. 168. Neuchatel, 1835. 



