2/O THE OCEAN WORLD. 



very common on every shore, and have been remarked by fishermen 

 from the earliest times on account of their singular form, the dis- 

 position of their arms, which resemble the tail of a lizard, and by 

 the singularity of their movements. The general characteristics of 

 this remarkable group of Echinodermata, as described by Dujardin 

 and Hupe, are as follows : They are radiate marine animals creeping 

 at the bottom of the sea or upon marine plants. In form they 

 present a sort of coriaceous disc, which is either bare or covered with 

 scales, which contains all the viscera, and has articulated to it five 

 very flexible simple or branching arms, each supported by a series of 

 calcareous internal pieces j they are naked or covered with granules, 

 scales, or spines. The mouth is situated in the middle of the lower 

 surface of the disc, and opens directly into a stomach which is in the 

 shape of a sac ; it is circumscribed by five re-entering angles corres- 

 ponding with the intervals between the arms, having a series of 

 calcareous pieces, which perform the function of foot jaws. The 

 mouth is prolonged by five longitudinal clefts, which correspond to 

 the arms, and are garnished with papillae or calcareous pieces. A 

 series of calcareous pieces, somewhat rib-shaped, spring from the 

 extremity of each of these clefts, which occupy all the interior of 

 the arms, having a furrow in the middle of the ventral surface for 

 the reception of a nutritive vessel ; and laterally between their ex- 

 pansions are certain openings, from whence issue the ambulacral 

 feet ; the visceral cavity opens by one or two clefts on the ventral 

 surface of each side of the base of the arms. 



The Ophiuridae move themselves by briskly contracting their 

 arms so as to produce a succession of undulations analogous to those 

 by which a serpent creeps along. Some of these Echinoderms are 

 rather active ; but others attach themselves by their arms to the 

 branches of certain Gorgonidae, and remain immovable for a consider- 

 able time, waiting their prey somewhat like a spider in the midst of 

 his web. 



The family of Ophiuridae is divided into two great sections : that of 

 the Ophiurinae, which comprehends several genera, amongst others 

 that which gives its name to the family; and that of the Euryalinae. 



The family of Ophiurinae forms a group distinguished by their five 

 simple, articulated, very mobile, and non-ramified arms, each of 

 which is attached to a small disc or shield plate, with flexible thread- 

 like cirri between the rays. The genus Ophiura is very common, and 

 has been known from very early times in European seas. The species 

 are often of a greenish colour, with transverse bands, which become 

 more obscure upon the arms as the distance from the disc increases. 



