112 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



and pedicellariae have assumed the fully adult reduction and concentration.] In 

 other words, some of the incentive to splitting may be due to a sort of physiological 

 duality locked up in the young with six rays. The five-rayed young with one madre- 

 porite would naturally be derived from larvae with one hydropore. Possibly the 

 five-rayed young with two or three madreporites are descended from incompletely 

 twinned larvae; or again they may already have accomplished the reduction division 

 without showing outward signs. 



Although the mechanics behind this curious condition are as yet material for 

 speculation, the phenomenon itself seems to produce a fairly definite asexual genera- 

 tion following close on the heels of the larval stage. This asexual mode of reproduc- 

 tion is associated with an abnormal symmetry for the genus. 



Young phase of S. alexandri (Ludwig). — This was described as Eydrasterias 

 diomedeae Ludwig. 47 I have examined four specimens from the following stations: 

 One from station 3368, near Cocos Island, 66 fathoms, rocky, R 6.5 mm. Three 

 from station 3397 (at which adult alexandri were taken), Gulf of Panama, 85 fathoms, 

 green mud, broken shells (R 20 mm.). See Plate 81, Figure 6. 



Ludwig records seven specimens in all, of which six are six-armed and one 

 seven-armed (with four large and three small rays). All are regenerating three rays. 

 These specimens differ from the adult in the same features that have been detailed 

 above for euplecta. Furthermore the young stage resembles that of euplecta much 

 more closely than does the adult that of euplecta. The crossed pedicellariae are 

 figured for comparison with those of the adult, (pi. 52, figs. 2, 2a.) 



Ludwig in the same brochure, (p. 246, pi. 35, fig. 205) describes without naming 

 a new species of Eydrasterias from station 3404, at which the incomplete type of 

 Distolasterias robusta (Ludwig) was taken. There are nine arrns but no disks. They 

 appear to me to represent a young phase of D. robusta. 



SCLERASTERIAS HETEKOPAES Fisher 



Plate 43, Figure 2; Plate 52, Figures 3, 3a; Plate 53, Figures la-Id; Plate 54; Plate 56, Figure 2; 



Plate 81, Figures 1-5 



Sclerasterias heteropaes Fisher, The Genus Sclerasterias Perrier, Bull. Inst. Oceano- 

 graphique, Monaco, No. 444, 1924, p. 7, text-fig. 2. 



Diagnosis. — Rays five, frequently unequal, constricted at base, pentagonal in 

 section, very gradually tapering to a blunt extremity; dorsolateral surface of ray 

 steeply sloping as a rule; intermarginal face wide, vertical. Spines in fairly regular 

 series; carinal and superomarginal with one spine on alternate plates; dorsolateral 

 spines usually few or absent, in one series if present; two inferomarginal spines; 

 actinal spines few or absent; dorsal spines terete, tapering, blunt; superomarginals 

 a little longer; inferomarginals compressed, often truncate, at tip; oral spines often 

 narrowly to fairly broadly spatulate and gouge-shaped; crossed pedicellariae in con- 

 spicuous circumspinal wreaths; absent from actinal and inner inferomarginal spines; 

 straight pedicellariae few, small, lanceolate, toothless. R = 90 mm.; r = 12 mm.; 

 R = 7.5 r, breadth of ray at base, 13 mm. 



Description. — In most specimens the ray is pentagonal in section, the carinal 

 plates marking the odd angle of the pentagon. The dorsolateral areas slope more or 

 less steeply to the superomarginal angle, the intermarginal areas being broad and 

 nearly vertical. In the type there are three dorsal series of spines, namely, the carinal 



" Mem. Mus. Comp. Zool., vol. 32, 1905, p. 242, pi. 34, flg. 201; pi. 35, fig, 206. 



