A. M Verrill — Worth American Ophiuroidea. 321 



corals, or lodged among their branches ; others have occurred on 

 hydroids ; certain species, like 0. fraterna and 0. bidentata, often 

 occur in vast numbers in the dredge where the bottom is composed 

 of broken shells, covered with hydroids, sponges, crinoids, etc., 

 among which they evidently find shelter ; some species, as 0. gracilis 

 and 0. pentacrinus^ cling closely to crinoids. 



It seems, therefore, that most of the species live more or less ex- 

 posed to the attacks of fishes and other active enemies, against 

 which a covering of sharp spines would aiford some protection. But 

 as fishes avoid coral-animals and hydroids, on account of their 

 stinging powers, it might be expected that those species living 

 among the branches of such organisms would require less protec- 

 tion by spines than those that merely conceal themselves, more or 

 less, among the debris of the sea-bottom. A more careful study of 

 the habits of the shallow-water species may determine, hereafter, 

 whether such differences in habits have determined the evolution of 

 the spines of the disk. 



As for the long arm-spines, characteristic of most of the species of 

 this and allied genera, they appear to have been developed in nearly 

 all genera that habitually live exposed,* while those genera that live 

 buried in the mud or sand, like OphioglypJia, Ophiomusium, 

 Amphiura, Amphipholis, etc., or securely hidden in crevices or 

 under stones, genei'ally have short arm-spines. 



Some of the species of OpMacantlia are brilliantly phosphorescent 

 when first caught, I have myself observed this to be the case with 

 0. bidentata, 0. fraterna, and others. It may, very likely, be a 

 peculiarity of the deep-water species, if not of all the others. 



Owing to the difficulties in the way of the ready identification of 

 the species, I have prepared the following analytical tables, which 

 ought to aid materially in locating any of them, if the specimens be 

 full grown, or nearly so. The young often differ considerably from 

 the adults in the number and roughness of the arm-spines, armature 

 of the disk, etc. The number of arm-spines counted is that of the 

 largest groups, near the base of the arms; farther out the number 

 rapidly decreases. The number of oral papilhe often varies with age, 

 and also individually, in many species, especially in those in which 

 they are numerous and clustered. The number of tentacle-scales, 



* The genus Ophiothrix is notable for the high development of its spines. The 

 species usually live more or less exposed, clinging to sponges, gorgonians, etc., 

 which they often closely imitate in color, biat some species live in the internal 

 cavities of sponges. 



