A. E. Verrill — North American OphiuToidea. 305 



The more typical of these genera have the disk-scales covered 

 with slender rough spinules, but the number and length of the 

 spinules may vary considerably, even in the same species of Ophio- 

 thrix. Some of the genera have only granules on the disk-scales, 

 and others have naked scales, and some even smooth skin. 



Nearly all the genera and species of this family live clinging 

 closel}^ to various sponges, gorgonian corals, crinoids, hydroids, or 

 even to other ophiuroids. Many of them ai-e more active in their 

 movements than is usual among Ophiuroidea, and many are bright 

 colored when living. 



The genus Opliiop>teron Ludw. is very remarkable for having a 

 broad membranous web between the arm-spines, and is supposed to 

 be a free-swimming form. It is from Amboina. 



The species of this family are mostly found in the warmer seas 

 and in shallow water, and they are most abundant and most diver- 

 sified in the East Indies. Brock enumerated fifty-six species of this 

 family from the Indo-Pacific region and considerable additions have 

 been made to the list by later writers. Several of the genera are 

 known only from the East Indies or Australia. Ophiothrix is the 

 only West Indian genus. 



Family, AMPHIUBIDiE Ljung., 1867 (emended). 



Amphiurida Verrill, Oph. Bahama Exp., Nat. Hist. Bull. Univ. of Iowa, v, 

 p. 23, 1899. 



In the report on the Ophiuroidea of the voyage of the Challenger, 

 Mr. Lyman, 1882, recognized about ninety species of Amphiura. 

 In subsequent papers by him and others, about thirty additional 

 species have been described. This very extensive assemblage of 

 species is evidently capable of being divided into several natural 

 groups, in addition to the several minor groups already separated by 

 Mr. Lyman and others. Mr. Ljungman, as long ago as 1867, set oif 

 a large number of species as a natural generic group, under the 

 name of Amphipholis. At a still earlier date, Liitken had indicated 

 this and other natural sections of the genus, without naming them. 



Ml". Lyman, however, did not recognize Amphipholis and some 

 other good divisions in any of his works, except as sections of the 

 genus. 



The contrast between the structure of the mouth in typical Am- 

 phipholis and typical Amphiura is very striking. The oral papilla} 

 in the former can close up the mouth-slits tightly, acting like oper- 



