SKUl'EXT STARS. 149 



In typical Oi>hiur.ans tho moutli, just .ilicive tin- tcctli, <)]ieiis In- a round, contrac- 

 tile aperture into n lar>>e, Hattencil stdiuach, which spreads over tlie basis of the arms 

 and into the inter-l)raehial spaees. Tliciu-li sometimes a iitth' wrinkled, it is usually 

 destitute of pouehes, convolutions, or ciecal appendages. IJetween the stomach and 

 the disc wall lie the i-eproduetive organs, consisting of elongated hags communicating 

 « ith closed tubes, which bear the o\ a or sjiermatozoa. In the Astrophytidte the 

 upper part of the stomach is surrounded by numerous radialiuL;- folds or bags, which 

 are attached to the roof of the disc, to the genital organs, and al tm points encircling 

 the mouth. The body cavity would thus l)c divided into ten parts were it not for the 

 open si)ace or canal which runs around tlu' mouth, and corresponds to the ring-canal 

 of a true Opbiui-an, but differs in lieing a continuation of the body cavity instead of a 

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

 cavity is the neuit.al cavitv. .nul an ovarial lobe oj)ens into each compartment. 



Lyman emimerates aliout five hundred species of Ophitn'oidea, fi^rty-nine of which 

 are Astrophytida'. Although but few of tlie sub-order can be reg.arded as littoral, 

 nuire than half, or two hun<lird and scxculy-eighl species, are found above the depth 

 .of 30 fathoms, and two hundred and tweuty-si\ of these do not occur in deeper water. 

 Thirty-eight of the remaiuiug coast species do not descend beyond 15U fathoms, 

 twelye others reach to .'.(III, and only two ^o low'i'r than r>l)0, but do not reach 1,000 

 fathoms, lietwei'n oO and l.")(l fathoms one hundred and tifty-one s]>ecies occur, 

 sixty-nine of which ai'e not f<unicl 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 si.xty-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 subse<pient dredgings, but even now we know of fifty exclusively dee]>-wnter 

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



In the genus Op/dura the disc is coveiicl with small granulations, which more or 

 less covers the snndl, oblong, .separated radi.il shields: the jaws are set with teeth; the 

 sjiines, which are on the outer edges of the side arm-]>lates, and parallel to them, are 

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

 are four genital openin'_;s. A fine s|ieeies is O. fi'/rx. from Lower California and the 

 west c(jast of Ceutr.al America. 



PKctiuui-d is another large genus, distingnislied from OyVu'/MVi by tlie absence of 

 the a<lhesion of the edges of the genital openings that, in the latter geinis, doubles 

 their number. In Opliiozona the larger scales of tlu' disc are intermingled with 

 lines of smaller ones, while OpJiioceramis has none of tiiesi' sm.dl scales, Vmt is known 

 by large mouth-frames, develojjed into wing-like ])rojections, and by a very long and 

 large first arm-bone of unusual form. Ophio/jli/pha is a genus with fifty-eight known 

 species, all of which have numerous tentacle scales, whih' the ]iair 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 Ophiocte)i the side arm-j)lates are large, meeting below the arm, liut not above; 

 while in Ophiomusiuin both njiju'r and under arm-plates arc so small that tlie side 

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

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

 O. 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 



