24 ASTROTOMA AGASSIZII. 



regularly imbricated scales. Under the skin may lie found the radial shields, 

 which are perhaps smaller than in any other apeciea among OphiuridcB. 

 There are no upper arm-plates, nor do the side arm-plates meet above ; 

 a want which is not found even in Opteomyxa, whose upper arm-plates are 

 divided in several pieces, alter the analogy of OpMopbcus, and are covered 

 by a thick skin. 



ASTROTOMA* gen. nov. 



Disk and arms granulated. Radial ribs low and narrow, running to centre 

 c if disk. Arms simple, and traversed by annular ridges bearing microscopic 

 spines. Tentacle-spines stout, erect, standing by all the pores except those 

 close to the mouth. No mouth-papillae. Teeth and tooth-papillae similar and 

 spiniform, arranged in a clump at the inner point of the mouth-angle. Two 

 genital openings lying at the outer corners of each interhrachial space. 



This simple-armed Astrophyton resembles Astronyx in its dentition, while 

 in the covering of the disk and arms and in the tentacle-spines it is between 

 Astroschema (PI. IV. f. 57, 68) and Astrogomphua. 



Astrotoma Agassizii Bp. uov. 

 PI. IV. f. r,?-56. 



Special Marks. — Radial ribs slightly marked. Disk finely granulated ; the 

 under side of arms and surface round mouth more coarsely granulated. 

 Tentacle-spines three or four; short, thick. Blightly Battened, standing erect. 

 Upper surface of arm with low annular ridges which hear microscopic spines. 

 i me madreporic shield. 



/>■ cription of an Individual. — Diameter of disk, 20 mm ", Width of arm with- 

 out -pine-. 1""". Length of arm aboul 138 Tooth-papillaa and teeth 



represented by a olnmp of more than a dozen short, stout, sharp spines, like 

 those of Astrophyton, and arranged at the inner apex of the mouth-angle, 

 which ha- no -jiinc- near it- outer corner-. Arms cleanly rounded above ij 

 Battened below, where the} an' covered by a -month granulation extending 

 to the mouth region, which is separated from the interbrachial spaces by 

 lines of coarser grain- connecting the bases of the arms ;it the point where 

 thev blend in the disk. The arched upper surface of the arm is divided into 



* iitTTr/ft. ttnr , Tn/iij. nit 



