28 ASTROPHYTON POURTALESII. 



Astrophyton Pourtalesii sp. nov. 

 PI. IV. f. U-AS. 



Special Marks. — Disk round and tiesli}-, covered bj a thick skin, through 

 which show numerous grains on the upper surface. Three or four tentacle- 

 spines to each joore, extending to within one or two pores of tlie mouth. 

 One madreporic body, often covered by the skin, and situated at the inner 

 angle of the interbrachial space. 



Description of an Individual. — Diameter of disk, Go"""'. Width of arm where 

 narrowest within the disk, 8™"-. Width of largest branch, outside disk, 8"'"-. 

 Total length of arm measured along its branches, 204°""-, to wit : 1st fork 

 (which is within the disk) to the 2d (which is outside), 16°"°- ; 2d to 3d, 

 32"" ; 3d to 4th, 30"™-; 4th to Sth, 27""'- ; 5th to 6th, 29""-; 6th to 7th, 

 27mm.. 7t|j j-Q g,-!^^ ;^5mm.. g^ij ^-o 9(.1j^ lo"" ; 9th to 10th, T""-; 10th to 11th, 



7""" ; 11th to end, 4'™'-. Mouth-papillaj, teeth, and tooth-papillae all similar 

 and spinifoi-m ; small, nearly equal, and about a dozen to each mouth-angle. 

 Arms smooth, covered with thick skin, and rounded. The terminal twigs 

 have their joints marked by annular ridges {Fig. 4.3), which bear a double row 

 of minute spines, folded down on the ridge, and alternating with one another. 

 Disk fleshy, nearly circular, and covered by a thick skin ; the radial ribs 

 slightly marked. There are neither sj^ines nor stumps, but a quantity of 

 scattered granules, which are most plenty near the centime of the back, and 

 are almost wanting in the lower interbrachial spaces. At the inner angle of 

 one of the interbrachial spaces is the madreporic shield, which is so covered 

 by skin as to be hard to distinguish. Three or four tentacle-spines on all 

 the larger branches ; shoi't, blunt, spiniform, of equal size ; about 2°"" long. 

 On the two pairs of pores nearest the mouth, no spines, or only a single one ; 

 the following three or four pores have two spines each ; and those beyond, 

 three or four. Each pore on the terminal twigs has but two tentacle-spines, 

 in form of strong spiny stumps covei'ed with skin {Fig. 43, q), close to which 

 the tentacle {q) protrudes. 



Color, in alcohol, nearly white. 



A larger specimen had the disk 75'°°- in diameter. The distances from one 

 fork of the arm to the next were as follows : 1st to 2d, 14™"'- ; 2d to 3d, 

 29'°°' ; 3d to 4th, 27'°'" ; 4th to 5th, 29"""- ; 5th to 6th, 21'°'°- ; 6th to 7th, 

 IS-"-"-; 7th to 8th, H-""-; 8th to 9th, 14""" ; 9th to 10th, 10""" ; 10th to 11th, 

 lO'""-; 11th to 12th, S""; 12th to 13th, 7"'"'-; loth to end, 7"'"'- ; in all, 



