A. E. Yerrill — North American Ophmroidea. 353 



0. exigua (Lym.). Disk-scales few, coarse, with few thorny stumps. 

 Arm-spines six, rather short, tapered ; oral papillaB three, the outer 

 one on the adoral shield. Tentacle-scale one. 



The last named species should, I think, be referred to Ophio- 

 thammts, with which it agrees well in all external characters. (See 

 p. 350.) 



0. N'ormani Lym., omitted from the table, is to be referred to 

 Ophiacantha (typical group) as already stated (p. 349, note). It has 

 small and rather widely separated radial shields and four smooth 

 arm-spines. 



Opliiom.itra valida Lyman. 



Ophiomifra valida Lyman, Btill. Mus. Comp. ZooL, i, 10, p. 825, 1869; op. cit., 



X, p. 264, 1883; Lyman, 111. Cat. Mus. Comp. ZooL, vi, pi. ii, figs. 4-6; 



Lyman, Report Voy. Challenger, ZooL Ophmroidea, v, p. 209, pi. xli, figs. 



4-6, 1882. 

 Ophiomitra cervicornis (young) Lyman, 111. Cat. Mus. Comp. ZooL, viii, pt. li, 



p. 14, pi. ii, figs. 19, 20, 1875 ; Bull. Mus. Comp. ZooL, vol. v, part 9, p. 231. 

 Ophiomitra valida Verrill, Ophiur. Bahama Exped., Bull., v, p. 58, 1899. 



Several large specimens of this species, sent by Mr. Lyman, differ 

 considerably from his figures and description, which were made from 

 immature specimens. 



The most important differences are found in the moiith-parts. 

 The lai'gest of our specimens have very numerous oral papillae and 

 tooth-papillae, ci'owded together in clusters, very much as in Ophio- 

 camax. The tooth-papillae often consist of a row of three, on or 

 below the margin, and of two or three pairs above these, next the 

 teeth, but frequently they are so crowded that no such regular 

 arrangement can be made out. There may be as many as nine or 

 ten on one jaw-apex. The distal oral papillae form crowded groups 

 of four to seven, or more, or they may stand in two rows, so as to 

 cover or conceal most of the width of the jaw. They are all rather 

 stout, spiniform, subacute. The distal oral tentacle-pore is large, 

 marginal, exposed, nearly surrounded by sheath-like processes of the 

 jaw and first under arm-plate, which is small and deeply concave. 

 The oral tentacle is large, with a thickened basal part into which 

 the distal part can be retracted. 



Tentacle-scales two or three on the basal joints ; farther out the 

 pores and scales decrease in size rapidly. On the basal joints the 

 inner scale is large, flat, lanceolate, erect, hollowed out on the side 

 next the tentacle; the other is narrow, subacute. The under arm- 



