OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 181 



I have previously described and figured ('05, p. 68, pi. 4, fig. 37) 

 the arrangement of the peripheral plates of the dorsal surface of the 

 disk ; these stop rather abruptly at the periphery, and often form a 

 distinct marginal row. This character is seen on the photograph 

 which I give here (pi. 71, fig. 8). Sometimes even the plates of this 

 marginal row are turned upward so as to stand more or less erect, 

 and then they recall the character on which the genus Ophiophrag- 

 mus was based. This arrangement is even more pronounced in the 

 majority of the Albatross specimens than in those which I have had 

 occasion to study heretofore, and because of this external resemblance 

 to the genus Ophiophragmus I was anxious to determine whether 

 the internal structure of this last genus, which is, as is known, very 

 characteristic, was found in A. relictus. 



On plate 70, on figure 8, I give a photograph of a specimen of 

 which the dorsal surface of the disk has been removed and which 

 has been prepared to show the peristomial plates with the adjacent 

 parts, as well as the internal and external genital plates. If this 

 photograph be compared with the figure published by Lyman of 

 Ophiophragmus wurdemani ('82, pi. 40, fig. 4), important differences 

 are immediately noticed, and, on the other hand, it is found that 

 there is much analogy with the figures published by authors of 

 species of the genera Amphiura or Amphioplus (compare for exam- 

 ple the figure of Amphiura bellis given by Lyman in fig. 16). Re- 

 garding the genital plates, the internal plate, or adradial, of A. 

 relictus is very stout, thick, and stubby ; it is rather short, and does 

 not exceed, or scarcely reaches, the third vertebra ; the external geni- 

 tal plate, or interradial, is very small, narrow, and still shorter than 

 the other, and it does not exceed the fourth vertebra. 7 We may also 

 compare this arrangement with that which Duncan has described and 

 figured in Ophiophragmus affinis. In the figure which he published 

 in 1886 ('86, pi. 8, fig. 6) we find that these two plates are much 

 elongated; they reach the first vertebra, and they remain very nar- 

 row. Duncan's figure, though schematic, should be exact, for the 

 author says (p. 89) in regard to the characters of the genus Ophio- 

 phragmus: " The genital plate is long and slender, and simply ' knob 

 headed,' and the generative scale is long and slender and longer than 

 the plate." 



7 Authors habitually use the terms " scale " and " plate " to designate the plates which 

 I call, respectively, "outer genital plate" (or "interradial") and "internal genital 

 plate" (or "adradial"). I believe that the terms "scale" and "plate" may lead to 

 confusion, as they are sometimes used indifferently one for the other ; some authors call 

 " scales," others " plates," the structures which cover the disk ; that is why I prefer to 

 use the word " plate " only when followed by an adjective indicating the position of the 

 plate when that is necessary, but as for the most part in systematic descriptions the 

 characters furnished by the interradial plate alone (genital scale) are used it is to that 

 that I apply always and exclusively the term "genital plate" without further designation. 



