Introduction to Animal Morphology. 133 



res 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, which has the large disc and 

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

 and arms ; or they may nut 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. 



: . ( )phiurida3 arms unbranchecl, shielded ; ventral grooves 

 red with plates ; genital slits usually 5; madrcporiform 

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

 ra, in nine sub-families. Ophioderminae mouth-edge 

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

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

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

 rachna). < )phi<culccinae disc naked; mouth-edge papil- 

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

 cral papilla; present (( )pliioblenna), or absent (Ophioscolex). 

 .lomyxinx tooth papilla; present ; mouth edge papillose ; 

 tly (Ophiarthrum) or naked, the tips only 

 rough spines bring free (Ophiomyxa). Ophiothricinae 

 mouth ; ipillosc ; disc with multangular spines 



{Ophiunyx}, or with granules, hairs, or spines, and hook-like 

 MCS on the arms (Ophiothrix). Ophiocomince mouth 

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

 : tOQth papilhu present; disc granular; arm 

 .'.her constantly visible or seen when the body dries 

 . < phiacanthinae like the last in many 



: Ided and granular dise, but with no tooth 

 papil' with large lateral shields. Ophiuner. 



witi. .tli minute shields ; arms 1 



narrow at origin ; radial shields overed. Amphiuriiuv with 

 lial shields, and keeled lateral am < )phi<>- 



:i ally shielded ; tori angiilares n.i' 

 nth sliirlils 1. :1 slit papillose. The 



