12 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Among the genera established by Matsumoto the two genera Aspi- 

 dophdura and Ophiurolepis are similarly very well characterized, 

 but they only include a very small number of species — four in both 

 combined. The genera Amphiophiura and StegopMura both include 

 species in which the disk is thick and in which the dorsal and ventral 

 arm plates are well developed and in contact throughout a large 

 portion of the arms ; the ventral arm plates especially are large, often 

 as long as broad, and they cover a relatively large portion of the ven- 

 tral aspect of the arms. Matsumoto differentiates StegopMura by 

 the short arms which are very broad at the base and diminish very 

 rapidly in breadth, while in Amphiophiura the arms are rather nar- 

 row, but in compensation longer and diminishing gradually in width. 

 While the characters cited by Matsumoto are easy of application in 

 a certain number of species, it is not the same for others, and the 

 limits off the two genera are indefinite. This is one of! the weak 

 points of Matsumoto's classification, and here there are certain to 

 arise doubtful cases, leading to differences of opinion among zoolo- 

 gists. I see already an instance in the case of 0. solida Lyman, which 

 Matsumoto placed in the genus Amphiophiura ('15, p. 77), while 

 H. L. Clark assigned it to the genus StegopMura ('15, p. 317). The 

 species is retained in Amphiophiura by Matsumoto in 1917. More- 

 over, Matsumoto himself states that the rather numerous species as- 

 signed by him to the genus Amphiophiura form four groups which 

 in their characters approach, respectively, the genera Ophiopyrgus, 

 Aspidophiura, StegopMura, and Ophiura (in the restricted sense). 



Matsumoto has left in the genus Ophiura all the species not 

 assigned to the four genera established by him, and in which the disk 

 and the arms are flattened, the ventral arm plates are very short, the 

 tentacular pores are well developed, the mouth pores are very large, 

 provided with numerous scales, and close to the mouth, etc. I men- 

 tioned above that certain species retained by him in this genus as 

 restricted had been removed by H. L. Clark and placed in the genus 

 Eomalophiura (O. abyssorum, O. confragosa, etc.). In my opinion 

 certain other species retained by Matsumoto should also be removed 

 from the genus Ophiura (in the restricted sense), some to be placed 

 elsewhere, others to be definitely suppressed. For example, O. 

 hexactis does not belong to the genus Ophiura at all, but to the genus 

 Ophionotus, as I showed in 1912 and as I have confirmed in a more 

 recent work ('17, p. 61), where I have given new evidence of the 

 correctness of this disposition based upon the characters of the peri- 

 stomal plates; 0. nana Liitken and Mortensen is a synonym of my 

 O. inflata described three years earlier, and the name therefore must 

 disappear from zoological literature, while the latter species should 



