MORPHOLOGY. 



I.— GENERAL INTRODUCTION. 



The Comatulse constitute a group of Neocrinoids, which is so extensive, and differs 

 so much from the remaining members of the order, that a subordinal rank may not 

 improbably come to be assigned to it. The great variety and extensive distribution of 

 the species of Antedon and Actinometra at the present time recall similar facts about 

 Pentacrinus and Millericrinus in the Mesozoic rocks, and about Actinocrinus and 

 Platycrinus in the Palaeozoic series. 



Although a few Palseocrinoids, such as Agassizocrinus and Edriocrinus, seem to 

 have been stemless and unattached in the adult condition, the enlargement of the top 

 joint of the larval stem into a cirrus-bearing centro-dorsal is not known to have 

 occurred in any Palaeozoic, or even in any Triassic Crinoid ; while the physiological 

 condition of the young Edriocrinus has been frequently reproduced in the Mesozoic 

 Holopidse and in the recent genus Holopus, which inhabits comparatively shallow 

 water in the Caribbean Sea, side by side with the free Crinoids or true Comatulae. 



The real nature of the latter group was long misunderstood. Linck and Linnaeus 

 followed Llhuyd in regarding them as peculiar forms of the Sea-stars, to which the general 

 name Asterias was assigned by the great Swede. Early in the present century, however, 

 the free Crinoids were separated from the Asterids and Ophiurids by Lamarck. But he 

 entirely failed to recognise their relationship to Guettard's Pentacrinus, which he placed 

 among the Polypes, together with the various species of fossil Crinoids. 



Five years before Lamarck wrote, the genus Antedon had been established by de 

 Freminville 1 for a Feather-star from tropical seas ; while in the next year Leach 2 united 

 all the known species of this type of the Echinodermata under the one genus Alecto. A 

 similar step was taken in 1816 by Lamarck, 8 who proposed the genus Comatula and 

 assigned to it eight species, six of them being new. One of these had been previously 



1 M«5moire sur un Nouveau Genre de Zoophites de l'Ordre des Radiaires, Bull. Soc. Philom. Paris, Bd. ii. 

 pp. 349, 350, 1811. 



2 The Zoological Miscellany, London, 1815, vol. ii. p. 61. 



3 Histoire Naturelle des Animaux sans Vertebres, ed. 2, Paris, 1816, torn. ii. p. 530. 



(ZOOL. CHALL. EXP. — PART LX. 1887.) OoO 1 



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