f EETOET ON THE ASTEEOIDEA. 73 



Incipient pedicellarisc, formed of two or usually three modified papillae, are present on 

 some of the plates. 



The anal aperture is subcentral, but very indistinct. 



The madreporiform body is of enormous size and of compound structure, being 

 apparently made up of a number of plates. It occupies a subcircular area extending from 

 the marginal plates to nearly midway between the margin and the centre of the disk, its 

 diameter being about 11 mm. The surface of this area is covered with paxillse, which 

 are larger and more widely spaced than the paxillse of the abactinal surface generally, and 

 have their spinelets radiating nearly horizontally. The striation furrows are thus hidden 

 from superficial view, but may readily be seen when the spinelets are removed. The stria? 

 are of simple construction, and may easily be abraded. Amongst the paxillse upon the 

 madreporite are a considerable number of simple pedicellarise, formed of three or four 

 thickened spinelets. In addition to its great size the madreporiform body is rendered 

 more conspicuous by being abruptly raised above the general level of the abactinal surface, 

 which causes it to have a button-like or "put on" appearance. 



The ambulacral tube-feet have a small flatly cpnical termination. 



Colour in alcohol, a bleached yellowish white ; with sometimes darker shades of dirty 

 grey, or even patches of light brown upon the disk. 



Localities. — Station 44. Off the coast of North America, east of Maryland. May 2, 

 1873. Lat. 37° 25' 0" N, long. 71° 40' 0" W. Depth 1700 fathoms. Blue mud. 

 Bottom temperature 36°'2 Fahr. ; surface temperature 5G°'5 Fahr. 



Station 45. Off the coast of North America, east of Delaware. May 3, 1873. Lat. 

 38° 34' 0" N, long. 72° 10' 0" W. Depth 1240 fathoms. Blue mud. Bottom tempera- 

 ture 37°'2 Fahr. ; surface temperature 49° - 5 Fahr. 



Remarks. — This species is distinguished from all the others by its rigid rectangular 

 rays, by the enormous and conspicuous madreporiform body, by the small and very com- 

 pact paxillse of the abactinal surface ; and by the small and indefinite spinelets on the 

 actinal surface of the adambulacral plates. The characters which separate it from Dytaster 

 nobilis are discussed in the comparative description of that form. 



4. Dytaster nobilis, n. sp. (PI. III. figs. 1 and 2 ; PI. XXXII. figs. 3 and 4). 



This form is nearly allied to Dytaster madreporifer, with which I at first ranked it as 

 a variety. On closer study I consider it to be a distinct species. It differs from Dytaster 

 madreporifer in its larger size, greater development of disk, and shorter rays, the respec- 

 tive dimensions being R = 132 mm. ; r = 29 mm. ; R = 4 - 5 r. The rays are broader and 

 more depressed, though with a more definite median carination. The paxillas are larger, 

 more distinct, and with fewer spinelets, which radiate from the small tabulum, the centre 

 of which is often void, and often provided with a central granuliform spinelet. The 

 crown of the paxilla has the appearance of being sheathed in a continuous membrane, con- 



(ZOOL. CHALL. EXP. PART LI. 1887.) 10 



