OPHIUROIDEA 637 



of arm 7.5 to 12 cm.: Long Island Sound northwards, from low-water 

 line to great depths; common towards the north; Europe. 



2. Amphipolis Ljungman. Disc small, without spines but covered 

 with scales; arms slender; outer oral papillae very wide, equal to both 

 the inner ones: 20 species; cosmopolitan. 



A. squamata (Delle Chiaje). Six oral papillae in each corner of 

 mouth, the outer two very wide; 2 scales to each tentacle; color gray or 

 yellowish; radial shields whitish; diameter of disc 2 to 4 mm.; length 

 of arm 20 to 39 mm.; viviparous: Long Island Sound northwards, from 

 low -water mark to 60 fathoms ; Europe. 



Family 4. OPHIACANTHIDAE. 



Aboral surface of disc with granules or spinelets, which more or less 

 conceal the scales; oral papillae present; plates of arm regular and 

 distinct, the lateral plates bearing hollow spines which stand out from 

 the surface: 20 genera. 



Ophiacantha Miiller and Troschel. Disc with small spines or 

 granules; oral papillae long, 7 to 16 being in each corner of the mouth: 

 about 100 species; cosmopolitan. 



O. bidentata (Retzius). Diameter of disc 8 to 15 mm.; length of 

 arm 40 to 50 mm.: Casco Bay and northwards, in 10 fathoms and more; 

 Europe; Bering Sea. 



Family 5. OPHIOTEICHIDAE. 



Plates on upper side of the arms small ; no oral papillae present, but 

 a prominent group of tooth papillae at apex of each jaw ; brachial spines 

 stand out from the surface of the arm: 15 genera. 



Ophiothrix Miiller and Troschel. Surface of the disc covered with 

 small spines and granules; radial plates large and triangular; 1 scale to 

 each tentacle: 100 species. 



0. angulata (Say). With a longitudinal stripe on upper side of 

 arm ; disc 8 to 12 mm. across ; length of arms 5 cm. ; color very variable, 

 purplish or greenish : Chesapeake Bay and southwards. 



Family 6. OPHIOMYXIDAE. 



Arms and disc without distinct and regular plates and covered with 

 a soft skin, so that the arms can be rolled in towards the mouth; oral 

 papillae present: 8 genera. 



Ophiomyxa Miiller and Troschel. Disc and arms covered with a 

 skin; arm spines short and but little imbedded in the skin: 12 to 15 

 species. 



0. flaccida (Say). Diameter of disc 15 to 25 mm.; color olive or 

 yellowish, sometimes very dark: Florida and West Indies. 



