Introduction to Animal Morphology. 133 



genital fissures ten, two in each interbrachial space ; arms 

 not shielded, usually branched ; abdominal groove closed by 

 a soft skin. The genital fissures may be in pits between the 

 oral shield, as in Asteronyx, Avhich has the large disc and 

 arms naked ; or as in Asteromorpha, which has a granular 

 disc and arms ; or they may not be in pits, and the arms un- 

 divided and disc granulated (Asteroschema), or deeply annu- 

 lated (Asteroporpa). The arms may be divided at the tips 

 only (Trichaster), or branching from the base (Astrophyton). 

 In Astrophyton verrucosum, there are over 200,000 joints in 

 the arm-skeleton, each with two nerve threads and several 

 muscles. 



2. Ophiuridce — arms unbranched, shielded; ventral grooves 

 covered with plates ; genital slits usually 5 ; madreporiform 

 plate fused with one mouth-shield. This includes about thirty 

 genera, in nine sub-families. Ophioderminse — mouth-edge 

 papillose ; oral shields large ; tori angulares and disc granu- 

 lated ; arms arising from notches in the disc ; genital fissures 

 20 (Ophioderma, Ophiocnemis) or 10 (Ophiopeza, Ophia- 

 rachna). Ophioscolecinae — disc naked ; mouth-edge papil- 

 lose ; tooth papillae none ; spines smooth, imbedded ; ambula- 

 cral papillae present (Ophioblenna), or absent (Ophioscolex). 

 Ophiomyxinae — tooth papillae present ; mouth edge papillose ; 

 disc naked ; arms scaly (Ophiarthrum) or naked, the tips only 

 of the rough spines being free (Ophiomyxa). Ophiothricinae — 

 mouth fissure not papillose ; disc with multangular spines 

 (Ophionyx), or with granules, hairs, or spines, and hook-like 

 spines on the arms (Ophiothrix). Ophiocominae — mouth 

 slit papillose ; oral shields small, round ; disc not notched 

 for the arms ; tooth papillae present ; disc granular ; arm 

 spines either constantly visible or seen when the body dries 

 (Ophiopsila). Ophiacanthinae — like the last in many re- 

 spects, with a shielded and granular disc, but with no tooth 

 papillas ; arms with large lateral shields. Ophionereinae — 

 with no tooth papillae ; disc with minute shields ; arms long, 

 narrow at origin ; radial shields covered. Amphiurinae — with 

 naked radial shields, and keeled lateral arm-scales. Ophio- 

 lepinae — disc symmetrically shielded ; tori angulares naked, 

 not granular ; mouth shields large ; oral slit papillose. The 



