A. M Verrill — North American Ophiuroidea. 349 



Ophiomitra Lyman. 



Bulletin Mus. Comp. Zool., vol. i, p. 325, 1869; Voyage Challenger, v, pp. 



202-209, 1882, pi. xlv, figs. 4-6, (anatomy). 

 Verrill (restricted), Oph. Bahama Exped., Bull., v, p. 57, 1899. 



This genus is very closely allied to Ophiacantha. The only 

 special distinctions given by Lyman are the larger size and naked- 

 ness of the radial shields and the naked or nearly naked scales of 

 the disk. 



Mr. Lyman also described the disk of the type-species as rounded 

 and cap-like, — a character due, perhaps, to immaturity, for in large 

 specimens of that species the interradial margins are incurved or 

 emarginate. 



When adult the type-species {0. valida Lym.)* has numerous 

 spiniform, clustered oral papillse and tooth-papillae. The distal oral 

 tentacle-pore is large and sub-marginal, partly sheathed by proximal 

 processes from the concave first under arm-plate and inner side of 

 the jaw. The adoral shields are very broad, but wholly proximal to 

 the small oral shields. The basal tentacle-pores are larger and fur- 

 nished with two prominent tentacle-scales. The large, broad radial 

 shields are largely in contact. The disk-scales are not large, of 

 nearly uniform size, without specialized marginal ones, and bear 

 coarse, short, clavate, thorny stumps. The arm-spines are numerous, 

 somewhat thorny and glassy. The dorsal arm-plates are slightly 

 separated by the side-plates. 



Most of the species subsequently described by Mr. Lyman and 

 others differ much from the type, in several characters. 



They neai'ly all have a single odd tooth-papilla and a simple row 

 of oral papillse, as in typical Ophiacantha. The interradial mar- 

 ginal scales are usually large and specialized. The radial shields are 

 often entirely separate and in some cases not particularly large. 



In fact, they have little in common with the type, except the 

 partial nakedness of the radial shields and disk-scales, — characters 

 also found in species of Ophiacantha.\ Therefore it seenis necessary 

 to subdivide the genus. 



"•*■ The specimens originally described and figured by Lyman were all immature, 

 and had not developed the true character of the mouth-parts. 



f One species (O. Normani) referred to this genus by Mr. Lyman does not 

 agree with it even in these characters, for the separated radial shields are no 

 larger and no more exposed than in several species of Ophiacantha, and its disk- 

 scales are granulated. In its arm-spines, which are smooth and only four in 



Trans. Conn. Acad., Vol. X. October, 1899. 



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