ASTROPHYTON AGASSIZII. 187 



each joint has its double vertical row of large, close-set grains ; alon^r 

 the upper surface runs a sunken line or furrow. Disk with interbra- 

 chial spaces below nearly naked, tiiough iK'aring a few points not easy 

 to see ; above smooth, with a few scattered conical points ; on the 

 margin a raised edge, separating tiie u])])er and lower surfaces, liadial 

 ribs large, prominent (particularly without), running nearly to the centre, 

 and bearing a number of irregular grains, and low, conical points ; len<'-th 

 to breadth, 30 : 8 ; height (above up})er surface of arm), 8""". Genital 

 slits with two to four large ilat grains along the (i(\y;G next the inter- 

 brachial space, and ending without in a blunt, conical point. Arm- 

 spines microscopic, hooked; most numerous at the tips of the branches; 

 Ibund in numbers as far as the fifth ibrk from the disk, ^vithin which 

 point they speedily disappear ; at tips of branches arranged in two 

 vertical rows, each spine standing on a rounded grain as a base. Ten- 

 tacle-scales spiniform, resembling mouth-papilUv, standing in a close 

 row ; commonly three, sometimes four, near the mouth onlj- two or 

 one ; they extend, though fewer and smaller, as far as the inner end of 

 the interbrachial spaces. Color, in alcohol : arms and radial ribs light 

 yellowish-ljrown (near raw sienna) ; disk and interbrachial spaces below 

 dark purplish-brown. The living animal has the radial ribs yellow, and 

 the interbrachial spaces brown (Stimpson). 



Variations. — A smaller specimen, with a disk of 31""", had arms 

 with nine forks, of the following proportions : — 



From first fork to second, .... 13"""- 



second '• " third, 20 " 



" third " " fourth, 2;j " 



" fourth " '• fifth 14 " 



" fifth '• '^ sixth, 12 " 



" sixth '^ " seventh IG " 



" seventh '• '• eighth, 13 " 



eighth '' " ninth, 10 " 



" ninth " " end, 10 " 



133"""- 



The radial ribs were more regularly covered with short, conical spines, 

 than in the adult. In the interbrachial spaces above there were scarcely 

 any grains, but below and on the edge of the disk there were numerous 

 fine grains. The granulation of the arms was not so close as in the 

 adult, and was more confined to vertical ridges. A very young speci- 

 men, with a disk of 2"™, had arms 4.3""""- long ; there was but one Ibrk 

 in the arm, and this was at a distance of 2.2™"'- from the disk. Exce])t 

 for this fork, the specimen might have almost been mistaken for the 

 yoimg of Ojj/iiophoJis heJJis. The l)ack of the disk was covered with 

 about a dozen angular plates, which were separated by single rows of 



