BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



essential ones in determining the relative rates of calcification and 

 resorption. 



The total number of species included in the present report is 189, of 

 which 129 are here described for the first time. The number of 

 genera represented is 51, of which 12 seem to be entirely new, and one 

 other has been formed for a previously known species. At the same 

 time, the large amount of material available has enabled me to satisfy 

 myself that a number of species, hitherto accepted as valid, are really 

 identical with others either of earlier date or from which, owing to 

 insufficient material, they were supposed to be distinct. In this way no 

 less than fourteen names are relegated to the ranks of synonyms. As 

 many of the supposedly new North Pacific species are represented by 

 only a few specimens, often by only a single one and that in poor 

 condition, I have hesitated much over giving them names, but have 

 concluded that as a matter of convenience to later writers it is better 

 to designate them definitely, even though ultimately some of the names 

 have to be abandoned. 



In a few cases the question has arisen whether subspecies should 

 be recognized or not, but it has been invariably answered in the 

 negative, as our knowledge of ophiurans, their variation and their 

 distribution, is as yet too imperfect to permit any wise use of sub- 

 specific names. The situation is somewhat different as regards 

 varietal names, and I have made use of two such in connection with 

 the widely spread Ophiopholis aculeata which appears in the northern 

 Pacific in an extraordinary array of dissimilar forms. As no one of 

 the forms appears to be characteristic of a particular region it would 

 be inaccurate to regard any of them as subspecies, but as two of them 

 are very common arid easily recognized they are treated as varieties 

 of the typical form. 



A few details in regard to the collection may be of interest, even if 

 not of great scientific importance, and I venture to add them here. 

 Although there are altogether 189 species (and the two varieties of 

 OphiopJiolis aculeata referred to in the preceding paragraph), yet 

 more than three-fourths of the specimens are furnished by the fol- 

 lowing five species: 



