150 



LOWER INVERTEBRATES. 



Fig. 130. — OphiophoUs acideala. 



spaces, and thus seem to form part of tlie disc. It was found off Port Jackson in 

 30 to 35 fathoms. 



In all the foregoing genera, as well as in several others, the arm-spines are 



situated on the outer edges of the side arm-plates, 

 and are jjarallel to the arm, but in tlie remaining 

 genera the spines are set on the sides of tlie side 

 arm-plates, and stand out at a large angle with the 

 arm. The sjsines are thus much more conspicuous 

 than in the first group, and in many cases they are 

 not only long, but adorned with rows of small, pointed 

 teeth. In OphiophoUs the upper arm-])lates are sur- 

 rounded by a row of supplementary pieces, and the 

 lowest spine of the outer arm-joints is a hook. A 

 well-known species is O. aculeafa, which is found at 

 various depths, up to 400 fathoms, on the coast of 

 noi'theastern America and northern Europe, as well 

 as in the Arctic seas. It is often called 0. bellis, but was first described under the 

 name before given. OphiacHs, with twenty-four species, resembles the last genus, 

 but the upper ann-plates are with- 

 out the ring of supplementary 

 pieces. In both genera the arm- 

 spines are stout and smooth. O. 

 savignyi (0. viresceyis) is found 

 along the west coast of North 

 America, from Panama to Cape 

 St. Lucas. 



Ainphiura is the largest genus 

 of the order, since it contains eighty- 

 nine known species, all of which 

 have a small and delicate disc, cov- 

 ered with over-lapping scales and 

 showing the radial shields, and long, 

 slender, more or less flattened arms 

 with short spines of uniform size. 

 A. vmxiina, obtained by the Chal- 

 lenger expedition in 9° 59' S. lat. 

 and 139° A'l' E. long., at a depth 

 of twenty-eight fathoms, measures 

 nearly a foot across from end to 

 end of arms, though the disc only 

 slightly exceeds half an inch in 

 diameter. Ophiocnida differs from 

 Amphiura princiisally in the pres- 

 ence of small spines upon the scales 

 of the disc. There are, in fact, sev- 

 eral genera that are distinguished 

 from Amphiura by but slight characters, though the differences between the species 

 contained in those genera are cui-iously well marked and constant. Hemipholis 



Fig. 131. — Oplnactis sark/ui/i. 



