ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS — FISHER 53 



actinolateral spines are a little shorter, somewhat slenderer, but are often grooved. 

 There is considerable variation in the shape of these actinolateral spines but the 

 essential feature is that they are flattened, broadened, and when fully developed, 

 spatulatc. The spines and spinelets are borne on unusually prominent bosses or 

 condyles, which are more prominent than in any member of this family. Each 

 plate carries a number of spaced, slender, often basally curved, sharp, miliary spine- 

 lets 0.5 to 0.75 mm. long. These are rough, sometimes more or less flattened at the 

 tip, and are sheathed in life by a soft, not very thick skin which also covers the plates 

 and bases of the large spines.. Proximally the carinal plates carry 10 or 12 of these 

 spinelets; an adradial plate 3 or 4; a superomarginal plate about 7 or 8; the actino- 

 lateral plates, about 6. 



Pedicellariae numerous but not especially conspicuous. They are longer than 

 the spinelets but shorter than the spines, have round-tipped, subspatulate jaws, or 

 sometimes slenderer ones, and are variable as to numbers but stand on the edge of 

 the plates so as to be close to the papulae; each papular area has one or two of them 

 as a rule. For exact form see Plate 15, Figure 3. 



Ambulacral furrow wide; tube-feet four ranked the entire length of furrow. 

 Ambulacra] pores in four distinct alternating series. Adambulacral plates short 

 separated by muscular spaces about as long as the surface of plates. Prominent 

 plates with a transverse series of four or five, rarely six, slender spines of which the 

 first is well in the furrow and bears a terminal cluster of a few small pedicellariae or 

 one large one. The second and third are usually increasingly longer, reaching a 

 length of 3.5 mm. at base of ray; the fourth and fifth are short spinelets; sometimes 

 the fourth is about half to three-fourths the length of three. On the nonprominent 

 plates of the type are two or three spines. In a large specimen from station 4321 

 there are four and sometimes five, the outer two or three being spinelets; the second is 

 about the same size as the third spine of prominent plates, while the furrow spine is 

 shorter and often carries a fair-sized pedicellaria. "In the interradial angles are a 

 very few pedicellariae larger than elsewhere, and these may be 2 mm. long. Oral 

 plates short (as usual in Zoroaster) each with two marginal and two suboral spines, 

 1 to 2 mm. long; the distal marginal spine carries a cluster of three or four small 

 pedicellariae." (Clark.) 



Madrcporic plate subcircular, convex, about 2 ram. in diameter and situated 

 about halfway between center of disk and margin. 



Color of alcoholic material brown and brownish yellow; small specimens from 

 stations 4432 and 4433 were bleached vermilion when first received; later this color 

 disappeared entirely. In life they were probably bright red (which in the deep sea 

 is equivalent to no color). 



Anatomical notes. — This species has well-developed superambulacral plates. 

 As six fully grown examples of the northern race are available, notes on the soft 

 anatomy will be found below under Myxoderma platyacanthum rhomaleum. 



Young. — The smallest example (station 2960) has R 5.5 mm. and relatively 

 long slender spines. The adambulacral plates are as yet undifferentiated. A specimen 

 with R 20 mm. has the differentiation of the adambulacral plates well started, but 

 the actinolateral spines are still slender. An example from station 3201 with R 14 

 mm., when compared with a specimen with R 15 mm. from station 3112, and of the 



