104 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



the same form throughout the whole length of the arm in O. stultus, 

 which I described in 1904 ('04, p. 141) . The description of 0. dicyclus, 

 published by H. L. Clark (11, p. 181), makes no mention of this 

 modification, and neither Lyman nor Verrill have made any allusion 

 to it in speaking of O. exiguus. I shall describe further on a new 

 ophiuran collected by the Albatross, which I assign to the genus 

 Ophiurothamnus O. excavatus and in this, as in O. stultus, I do 

 not observe the least tendency for the first ventral spine to become 

 transformed into a hook in the terminal part of the arm (see pi. 22, 

 figs. 4, 6). 



Ophiothamnus laeiris thus differs from the other species now in- 

 cluded in the genus Ophiurothamnus by this transformation of the 

 first ventral spine into a hook in the distal region of the arms, which 

 was described by Liitken and Mortensen. Is this character suffi- 

 cient to make it necessary to take this species out of the genus 

 Ophiurothamnus and to place it in another genus? I do not think 

 so, more especially since the transformation into a hook, so far as 

 can be judged by Liitken and Mortensen's figure ('99, pi. 19, fig. 4) 

 is not very marked; there is not a true compound hook here, like 

 that which we have seen appear in Ophiotreta rtiatura and Ophien- 

 trema leucostictum, and which recalls that of the species of Ophio- 

 thrix' the modification is especially produced by the irregular and 

 unequal denticulations which are developed on one of the borders 

 of the ventral spine, in combination with a curvature of the tip. 



But, however that may be, it seems to me indispensable to remove 

 from the diagnosis of the genus Ophiurothamnus established by 

 Matsumoto the phrase relative to the transformation of the first 

 ventral spine into a hook, the more so as it only refers, as I have 

 just said, to a sort of imitation hook. To the four species which 

 Matsumoto has already assigned to the genus Ophiurothamnus O. 

 dicylus (H. L. Clark) (genotype), O. exiguus (Verrill), 0. stultus 

 (Ko3hler), and perhaps 0. laevis (Liitken and Mortensen) there 

 must be added the new species which I am describing below, and to 

 which I propose to give the name of O. excavatus. 



OPHIUROTHAMNUS STULTUS (Kcehler). 

 Plate 22, figs. 1-4. 



Ophiothamnus stultus KCEHLER ('04), p. 141, pi. 25, figs. 9, 10; pi. 26, fig. 1. 



H. L. CLARK ('15), p. 209. 

 Ophitirothamnus stultus MATSUMOTO ('17), p. 130. 



Locality. Albatross station 5660; Flores Sea; Cape Lassa, bear- 

 ing S. 88 W., 37.99 kilometers (20.5 miles) distant (lat. 5 36' 30" 

 S., long. 120 49' 00" E.) ; 1,266 meters (692 fathoms) ; December 

 20, 1909 ;gy. M., S. 



One specimen (Cat. No. 41194, U.S.N.M.). 



