270 bulletin: museum of comparative zoology. 



In size and superficial appearance, this little ophiuran is so much 

 like Amphipholis sqitamata, it was not until the mouth-parts were 

 examined that it was seen to be a true Amphiura. The further dis- 

 covery, which soon followed, that it is viviparous proved to be of 

 much interest and Dr. Mortensen secured an abundance of material 

 for the study of the development. Of previously known members 

 of the genus, A. stimpsonii seems to be as near as any to A. vivipara 

 and young A. sthnpsonii are very close. But the shorter and more 

 slender arms, the fewer, shorter, and differently shaped arm-spines 

 and the shorter and wider upper arm-plates seem to be constant 

 differences by which A. viripara may be distinguished from even very 

 young A. stimpsonii. 



This species swarms in the coralline Algae of Buccoo Bay, along 

 with two or three species of Ophiactis. I also found it common at 

 the Tortugas, Fla., in June, 1917. There is more or less diversity in 

 the yellowness of the coloration, for while the great majority are very 

 pale, distinctly yellow specimens sometimes occur. There is also 

 diversity in the duskiness of the arm-spines, for they may be very 

 distinctly marked, though as a rule they are uniformly whitish or 

 simply clouded with dusky. 



Ophiophragmus. 



Although this is not a large genus, its real character has been mis- 

 understood and a number of species have been referred to it errone- 

 ously. Lyman instituted the genus for three species described as 

 Amphiura but which differed from typical members of that genus and 

 agreed with each other in several important characters. Of these 

 characters the one on which he laid most stress, and from which the 

 name of the genus is derived, is the occurrence of a series of papillae 

 along the margin of the disk in the interradial areas. Duncan, 

 Matsumoto, and others have failed to recognize the important differ- 

 ence between this series of marginal papillae and the marginal "fence" 

 which occurs in some species of Amphiura, formed by the upturned 

 margins of the uppermost series of plates on the oral interbrachial 

 areas. This " fence " is well-developed in " Ophiophragmus" japonicus 

 Matsumoto but is not at all like the "fence" in true Ophiophragmus, 

 where it is composed of distinct papillae or spinelets. These may, 

 of course, be simply modified marginal scales but their appearance is 

 obviously different. 



More than a dozen species have been referred to Ophiophragmus. 



