OPHIUKANS OF UNITED STATES NATIONAL MUSEUM. 73 



manner. We should be very thankful to Verrill for trying to establish a primary 

 classification of these forms and to make in the genus OpTiiacantha some eliminations 

 which were necessary, owing to the steadily increasing number of the species attrib- 

 uted to the said genus. Unfortunately, the sections established by Verrill are most 

 unequal; if some may be preserved, as having the value of genera, others hardly 

 correspond to subgenera, or they are even very disputable and useless. That is 

 why Hubert Lyman Clark, when he studied, in 1911, the North Pacific ophiurans in 

 the collection of the National Museum, was impelled to write: "I am therefore 

 reluctantly compelled to ignore VerrilTs genera for the present and use OpTiiacantha 

 in a very wide sense." 



In fact, Verrill did use, as a basis for the sections introduced by him, some 

 characters which, at first sight, seem to have great value, but which practically offer 

 a very disturbing lack of constancy and accuracy. More especially the respective 

 size and the mode of arrangement of the oral or dental papillae, the shape of the 

 adoral plates, and the presence or absence of a distal lobe, which enables the said 

 adoral plates to separate the mouth shield from the first lateral brachial plate, the 

 state of the spines which form at the basis of the arms and on each side some rows 

 which dorsally are more or less approximate, the lesser or greater visibility of the 

 upper plate of the disk, are, in fact, characters which essentially alter with age, 

 and are sometimes found to vary in some specimens of the same size. I have 

 already had occasion several times to call attention to their inconstancy, and I 

 shall do so again farther on, when describing such species as Ophiacanfha anomala, 

 0. lidentata, OpTiiomitrella americana, etc. But, on the contrary, I am of the 

 opinion that the characters of the shape and armature of the tentacular pores, either 

 oral or brachial, which may vary considerably in shape and be either deprived 

 of or provided with scales having quite peculiar shapes and disposition, the 

 presence of genuine granules which extend up to the oral plates, the flattening and 

 widening of the brachial spines, etc., represent much more valuable structures; 

 consequently some of the genera established by Verrill, such as OpTiiopora, OpTiio- 

 limna, OpTiiopristis, seem to me to be perfectly justified. I have myself based 

 on some characters of the same sort such genera as OpTiiotrema, OpJiiomedea, and 

 Ophioleda. Verrill had also a very fortunate inspiration when he introduced some 

 sections (OpTiiacanfheUa, OpTiientrema) for certain forms, as OpTiiacantha troschdi, 

 tuberculosa, scolopendrica, etc., or when he separated from the genus Ophiomitra the 

 genus Ophioplinthaca. But how difficult it becomes to establish the limits of such 

 genera as Ophiotreta, OpTiiectodia, Ophientodia, Ophioscalus, etc. What is more, it 

 is just as difficult to establish a limit between the genus OpTiiomitrdla, created by 

 Verrill, and the genus OpTiiacantha, in the restricted meaning he gives to the latter 

 after having removed from it a whole series of forms, as it used to be to establish a 

 limit between the genera Ophiacanfha and Ophiomitra, when these two were taken 

 in a much wider meaning. In fact, when one carefully examines several species 

 which seem to be attributive to the genus OpTiiacantha, one can not help acknowledg- 

 ing, the presence, in most cases, on the upper face of the disk of very distinct plates, 

 if the teguments are somewhat thin, and especially if the specimen is dry. Is it 

 right, then, because these plates are small, to classify this example as an OpTiiacantha, 



