408 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The side arms, which are elongated and slightly projecting, bear 

 at first seven and then six small, short, papilliform spines, which are 

 situated along their distal borders; the number of the spines falls 

 rather rapidly to jive and then to four, and finally to only three. 



The tentacle pores number three pairs ; they are sometimes covered 

 by a large oval scale, and sometimes by two smaller scales ; the pores 

 of the first pair are rather large, and their size diminishes progres- 

 sively as far as the third pair. 



The color of the specimen in alcohol is whitish. 



Affinities and distinctive features. Ophiomusium impotent be- 

 longs to that section of the genus Opliiomusiuin in which the dorsal 

 and ventral plates persist throughout almost the entire length of the 

 arms. It shows some affinities with O. cancellatum Lyman, 0. cor- 

 ticosum Lyman, O. diomedeae Liitken and Mortensen, 0. properum 

 Koehler, and O. serratum Lyman, but it differs markedly from all 

 these species and can not be confused with any of them. Ophiomus- 

 i%m cancellatum has only two or three arm spines, and the dorsal 

 surface of the disk is covered with numerous imbricated plates: (9. 

 corticosum, which has, like O. impotens, numerous arm spines, has 

 four pairs of tentacle pores ; O. diomedeae has the mouth shields very 

 small; O. properum has only three pairs of tentacle pores, and its 

 arm spines are very different; O. serratum, which has four or five 

 arm spines, has the dorsal plates of the disk larger and less numerous,, 

 the mouth shields larger, the radial shields smaller, etc. 



OPHIOMUSIUM LIGATUM, new species. 



Plate 90, figs. 3-5. 



Localities. Albatross station 5445 ; east coast of Luzon, San Ber- 

 nardino Strait to San Miguel Bay; Atalaya Point, Batag Island > 

 bearing S. 56 E., 9.82 kilometers (5.3 miles) distant (lat. 12 44' 

 42" N., long. 124 59' 50" E.) ; 700 meters (383 fathoms) ; June 3, 

 1909 ;gn. M., S. 



One specimen (Cat. No. E. 80, U.S.N.M.). 



Albatross station 5650; Gulf of Boni, Celebes; Lamulu Point bear- 

 ing N. 5 W., 23.16 kilometers (12.5 miles) distant (lat. 4 53' 45" 

 S., long. 121 29' 00" E.) ; 987 meters (540 fathoms) ; December 

 17, 1909 ;gn. M. 



Two specimens (Cat. No. E. 81, U.S.N.M.). 



Description. The three specimens are of very large size and the 

 diameter of the disk varies between 20 mm. and 22.5 mm. ; one of the 

 arms of the specimen from station 5445, which is entire, exceeds 

 110 mm. in length. The habitus is very robust, and the individuals 

 recall very strongly O. trychnum, described by H. L. Clark from 

 specimens from Japan from depths varying between 128 and 1,057 



