OPHIURANS 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 Ophiacantha some eliminations 

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

 uted to the said genus. Unfortunately, the sections established by Verrill arc 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 opliiurans in 

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

 reluctantly compelled to ignore VerriU's genera for the present and use Ophiacantha 

 in a very wide sense." 



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

 characters wliich, at first sight, seem to have great value, but wliicli 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 papilla;, 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 sliield 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 

 ah-eady had occasion several times to call attention to their inconstancy, and I 

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

 0. hidentata, OpMomitreJla 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 bracliial, which may vary considerably in shape and bo either deprived 

 of or provided with, scales having quite pecuhar 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 struchires; 

 consequently some of the genera established by Verrill, such as Ophiopora, Ophio- 

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

 on some characters of the same sort such genera as Ophiotrema, Ophiomedea, and 

 OpUoleda. Verrill had also a very fortunate inspiration wlicn he introduced some 

 sections (OphiacantheUa, Ophientrema) for certain forms, as Ophiacantha troscheli, 

 tuberculosa, scolopendrica, etc., or when he separated from the g(>nus Ophiomitra the 

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

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

 is just as difficult to estabUsh a limit between the genus Ophiomitrelh, created 'by 

 Verrill, and the genus Ophiacantha, in the restricted meaning lie 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 Ophiacantha and Ophiomitra, when these two were taken 

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

 wliich seem to be attributive to the genus Ophiacantha, 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 OphiacantJia, 



