Boone, Echinodermata, Cruises of "Eagle" and "Ara," 1921-28 121 



July 21, 1927, collected by the "Ara," William K. Vanderbilt, com- 

 manding. Cat. no. 210. 



Color: In life the abactinal surface is reddish or reddish brown, 

 frequently maculated; the actinal surface is yellowish or whitish. 



Life history: The early stages of this serpent star have been 

 carefully studied. The larva is said to be clearly differentiated from 

 those of other closely related species by having fenestrated rods in 

 the posterolateral arms. The young attain sexual maturity in the 

 third year, at a diameter of 7 to 11 mm. 



Technical description: The "Ara" specimen figured is between 

 five and six years old. Disk diameter 25 mm., length of arm 71 mm. 

 The abactinal surface is covered with flat, irregular, overlapping 

 scales, the central one of which is circular and is surrounded by a sort 

 of rosette formed of primary and secondary scales, radiating from 

 this center, down the middle of each interbrachial space is a series of 

 larger, roundish scales overlapping smaller ones adjacent to the radial 

 plates. The radial plates are only about one-half as long as the disk 

 radius, widest just above the innermost dorsal arm-plate, where they 

 are contiguous or slightly separated, approximately pear-seed shape 

 with the apices directed inward. The outer arm-comb bears about 

 30 to 34 long, slender papillae. The interbrachial spaces of the actinal 

 surface are paved with irregular-sized, large, flat scales, those near 

 the lateral border being the largest. The genital slits are very long 

 and are outlined on the outer lateral wall by a long, flat scale, which 

 bears on its upper margin a fringe of fine short spinules. 



The mouth-shields are very large with the inner lateral margins 

 convergent, forming a triangle; the outer lateral margins are nearly 

 parallel the greater part of their length, converging outwardly with 

 the rounded outer margin. The side mouth-plates are long and nar- 

 row with the slenderer, outer distal angle reaching down to the genital 

 slit, inwardly the side mouth-plates narrow, but the tips, which are 

 triangular, do not meet. The mouth papillae are 18 to 21, acuminate, 

 of moderate size; 10 to 12 of these are clustered in two rows across 

 the apex of the jaw. The teeth are acuminate, the innermost one 

 slightly narrower and sharper than the others. 



The first under arm-plate is rectangular, about twice as wide as 

 long, well separated in the median line by a pair of large, pore- 

 shaped grooves. The second tentacle pore is outside the mouth-slit, 

 but opens into the mouth-angle. The second to eighth under arm- 

 plates are wide, triangular, each with the apex directed inward and 



