SERPENT STARS. 149 



In typical Ophiurans the mouth, just above the teeth, opens by a round, contrac- 

 tile aperture into a large, flattened stomach, which spreads over the basis of the arms 

 and into the inter-bvacluul sj)aoes. Though sometimes a little wrinkled, it is usually 

 destitute of pouches, couvolutious, or ccecal appendages. Between the stomach and 

 the disc wall lie the reproductive oi-gans, consisting of elongated bags communicating 

 with closed tubes, which bear the ova or spermatozoa. In the Astrophytidas the 

 upper part of the stomach is surrounded by numerous radiating folds or bags, which 

 are attached to the roof of the disc, to the genital organs, and at ten points encircling 

 the mouth. The body cavity woidd thus be divided into ten parts were it not for the 

 open space or canal which runs around the mouth, and corresponds to the ring-canal 

 of a true Ophiuian, but differs in being a continuation of the body cavity instead of a 

 closed, annular tube. There is no closed bag for the genital products, but the body 

 cavity is the genital cavity, and an ovarial lobe opens into each compartment. 



Lyman enumerates about five hmidred species of Ophiuroidea, forty-nine of which 

 are Astrophytida>. Although but few of the sub-order can )>e regarded as littoral, 

 more than half, or two hundred and seventy-eight species, are found above the depth 

 of 30 fathoms, and two hundred and twenty-six of these do not occur in deeper water. 

 Thirty-eight of the remaining coa.st species do not descend beyond 150 fathoms, 

 twelve others reach to 500, and only two go lower than 500, but do not reach 1,000 

 fathoms. Between 80 and 150 fathoms one hundred and fifty-one species occur, 

 sixty-nine of which are not found either above or below this range. Between 150 

 and 500 fathoms one hundred and thirty-seven species occur, seventy of which are 

 confined within these limits, while thirteen descend to below 1,000 fathoms, and 

 twenty to below 500. Only sixty-nine species occur below 1,000 fathoms, and of 

 these fifty do not occur above that limit. This number may of course be increased 

 by subsequent dredgings, but even now we know of fifty exclusively deep-water 

 species, living in water cold almost to freezing, and in entire absence of sunlight. 



In the genus Ophiura the disc is covered with small granulations, which more or 

 less covers the small, oblong, separated radial shields ; the jaws are set with teeth ; the 

 spines, which are on the outer edges of the side arm-plates, and parallel to them, are 

 smooth, flat, and shorter than the arm-joints ; side mouth-shields are present, and there 

 are four genital openings. A fine species is 0. teres, from Lower California and the 

 west coast of Central America. 



Pectinura is another large genus, distinguished from Ophiura by the absence of 

 the adhesion of the edges of the genital openings that, in the latter genus, doubles 

 their number. In Ophiozona the larger scales of the disc are intermingled with 

 lines of smaller ones, while Ophioceramh has none of these small scales, but is known 

 by large mouth-frames, developed into wing-like projections, and by a very long and 

 large first arm-bone of unusual form. Ophioglypha Is a genus with fifty-eight known 

 species, all of which have numerous tentacle scales, while the pair of tentacle pores 

 nearest the disc are slits of comparatively large size, surrounded by numerous tentacle 

 scales, and opening diagonally into the mouth slits. 



In Ophiocten the side arm-plates are large, meeting below the arm, but not above ; 

 while in Ophiomusium both upper and under arm-plates are so small that the side 

 arm-plates meet both above and below, while the radial shields and plates of the upper 

 surface of the disc are intimately soldered together, forming a surface like porcelain. 

 0. flabellum is a curious little form, with very short, rapidly tapering arms, and the 

 first pair of side arm-plates of each arm so large that they meet in the inter-brachial 



