8o Naturai. History Buli>i:tin. 



iiiiirr/i/iia in ha\-ing- a highly vaulted instead of a flat disk, as 

 represented in Agassiz' " Three Cruises of the Blake." and 

 described in the '• Blake " Reports. The arrangement of the 

 dorsal plates is also different. 



Next we have the genus Opiiiuiuxxa. which is placed on the 

 basket-tish side of the line. Our collection seems to contain 

 at least two species of this genus. Here we have forms with 

 the arm-plates and disk markings of the serpent-star replaced 

 b^■ a tough, leather^' membrane. The mouth-papilla? are 

 furnished with serrated edges, an approach to the spines in 

 this region characteristic of the basket-fish. The tentacle- 

 scales are obliterated, and the arm-spines are reduced to in- 

 conspicuous stumps. The radial ridges are not prominent. 

 A step farther is reached in the genus Opiiion-cas. of which 

 we secured at least three species at this station. This genus 

 has the astrophyton-like characters of Opliioiiiy.xa. and. in 

 addition the spiniform mouth-papilhe and prominent radial 

 ridges reaching in some cases clear to the middle of the dorsal 

 surface. The arms are immensely lengthened, reaching the 

 maximum of length to diameter to be found among ophiurians. 

 The three species secured may be differentiated as follows, the 

 W' riter not being willing to risk naming them : 



(a) A form in which one radial shield of each pair over- 

 laps its fellow. Length of arms to diameter of body is as 

 twelve to one. The color in alcohol is a decided brown. 



(b) An exceedingly slender form, with prominent but 

 narrow radial plates which do not touch each other. Length 

 of arms to diameter of disk as t\\'ent}'-Mve to one. This is a 

 small and delicate species, of a light pinkish brown color, 

 highlv vaulted disk, and remarkably attenuated arms . 



(c) A small but stouter form, with radial shields not reach- 

 ing to center of disk, but extending not much more than half 

 that distance. Disk flat; segments of arms very distinct, 

 much more so than in any other Ophiocrcas which I have seen. 

 Length of arms to diameter of disk as eight to one. 



Last of all we come to two species of Astroo-onipliiis, a genus 

 discovered by the " Blake " near the Florida Keys. This 



