KEPORT ON THE OPHIUROIDEA. 251 



arm, is a genital opening which, in most of the simple armed species, passes into a sac or 

 genital bursa ; but, in the ramifying species, enters directly the main body cavity. Most 

 of the simple armed have a mouth shield at the inner angle of each lower interbrachial 

 space, one of which serves as the madreporic. But, the ramifying have often no mouth 

 shields at all, and the madreporic plates, sometimes one and sometimes five in number, 

 are found in various regions of the lower interbrachial spaces. 



Astrophyton. 

 Adropliyton , Linck, De Stell. ]Mar., 1733. 



Disk re-enteringly curved in the interbrachial spaces, and, together, with arms covered 

 by thick skin. Arms extremely wide at their liase, so as to occupy a large part of the 

 disk, and branching by a series of numerous forks liaving between them short, and 

 nearly equal shafts. Eadial shields long and bar-like, composed of overlapping soldered 

 plates, and extending nearly or quite to centre of disk, thus forming more or less 

 elevated radiating ribs. A portion of interbrachial space Ijelow strengthened by 

 numerous plates. Teeth, tooth papillas, and mouth papillae, all similar and spiniform. 

 No arm spines, but the outer branches have spiniform. tentacle scales, which, as well 

 as tentacles, are wanting on the basal joints. The finer twigs only are ringed with 

 double lines of grains bearing microscopic hooks. Under side of arm entirely covered by 

 side arm plates. No under arm plates beyond the first ; and no upper arm plates at all. 

 Two short genital openings at the outer corners of each interbrachial space. 



In order to give a comparative idea of the geneva Asti vjihy ton, Gorgonocejihcdus, and 

 Euryale, there will Ije furnished some details of their skeletons. 



The radial shields of Astropliyton (PI. XXXV. fig. 18, I) are composed of soldered 

 overlapping plates, as in Gorgonocephalus, but differ in being higher and less diverging. 

 For the bracing of the broad, heavy arm there is on either side a massive, rounded 

 genital plate, shaped like an elongated cone (o). Its strength recalls the same part in 

 Euryale, as does the rudimentary genital scale (h) near its outer end. The distribution 

 of irregular plates under the disk skin is the reverse of that in Gorgonocephalus, which 

 has a compound row just along the margin, whereas in the present genus the plates, 

 which are large and flat, fill the inner angle of the lower interbrachial space (figs. 17, 18), 

 which thus becomes a structure more calculated to a;ive a strong leverage to the arm. 

 The mouth frames and jaws, broad, flattened and closely joined below (fig. 17, c), 

 become much narrower above (fig. 18, c), where there is a swollen, oblong jjeristomial 

 plate {v) of one piece. Their shape and massiveness recall Euryale (fig. 1, c), but the 

 bunch of spiniform tooth papillee is similar to that of Gorgonocephalus ; to which also 

 Astrop>hyton is comparable as to its small and irregular side mouth shields (fig. 17, h), 

 while those oi Euryale are of great size and thickness and nearly symmetrical (fig. 1, h). 



