ASTEROIDEA OP NORTH PACIFIC AND ADJACENT WATERS — FISHER 115 



The superomarginals might be described as kiteshape with arcuate sides, the descend- 

 ing half of the plate being very much larger than the dorsal half, and overlapping 

 the dorsal edge of the inferomarginals (the exposed surface of which is less than 

 half as large as that of superomarginals and occupies the sharp actinolateral border 

 of the ray. The superomarginals overlap (adoral edge outermost) and present a broad 

 lateral surface largely occupied by a roughly circular area of hyaline acorn-shaped 

 bosses closely placed, so that in an area with a diameter of 2 mm., 8 to 12 can be 

 counted in a line from one side to the other. In a specimen cleaned with caustic pot- 

 ash this area is conspicuously white against the smooth yellowish surface of the rest 

 of the plate. As in other members of this genus, only the alternate plates carry a 

 spine, but the hyaline area is about the same in all the plates. The inferomarginals 

 lack a marked ventral lobe. The principal lobe is dorsal, and underlies the descend- 

 ing lobe of the superomarginal. The plates are strongly imbricated and it is really 

 the obliquely oriented lower border which carries the two spines. The actinal plates 

 are rather thick subcircular disks with the margin to surface. The ambulacral 

 plates are not very compressed. There are 16 to 10 mm. in the type; in Stylast<r;<is- 

 forreri of the same ray-length there are 16; in Orthasterias lcoelileri, 20; in Leih- 

 asterias n. chelifera, 19 to 22. The pores have flaring lips and the two rows are a 

 little more widely separated than in Stylasterias. 



The actinostomial ring is stout and the actinostome small. The inner end of 

 the ambulacral ridge is as long as the succeeding six ambulacral plates. The first 

 pore is conspicuous though but little larger than the next three, which stand in a 

 triangular group. The interbrachial septum is calcified but very narrow on account 

 of the small disk. 



Viscera.— Intestinal coecum with two rather long unequal digitiform lobes 

 (without subdivisions). Hepatic coeca long. Gonads opening dorsally near inter- 

 brachial septum, on level with superomarginal plates. No Polian vesicles. 



Young. — There are two sorts of young: (1) Those which have five rays, the spines 

 essentially as in the adult (that is, single spines on alternate carinals and supero- 

 marginals), and the crossed pedicellariae in wreaths surrounding the spines. (2) 

 Those which are six-rayed, fissiparous, and have more than one carinal aud supero- 

 marginal spinelet; the crossed pedicellariae are scattered between the spinelets. 



Of the first sort there is a specimen from station 2934 with R as small as 20 mm. 

 It closely resembles the adult, but there is only a single dorsolateral (adradial) spinelet 

 on one ray. The madreporic body is relatively large and conspicuous, with numerous 

 fine striae — entirely unlike the small madreporites of-the fissiparous young. 



An example from station 2966 has one R 22 mm. The other four rays arc 

 regenerating and have R 10 mm. This is not a case of fissiparity, since the original 

 disk is intact. The new rays are of the adult and not the fissiparous sta^c. Ap- 

 parently once this immature stage is left it is not repeated in small regenerating rays 

 of the adult. No extremely small specimens in the adult phase were taken. These 

 are all in the fissiparous, predominantly six-rayed stage. 



Fissiparous stage. — Young specimens in the fissiparous stage were taken at the 

 following localities. 



