110 



BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



There are thus 36 specimens of which 9, or one-fourth, have five rays. Among 

 the 26 actively dividing specimens, none has five rays. Two five-rayed specimens 

 are definitely intermediate between the young and adult phases. Most of those 

 actively dividing have three small rays in various stages of regeneration. 



The outstanding features of this phase of euplecta are the scattered pedicellariae 

 and the more numerous spinelets. Each proximal carinal has usually three short 

 subclavate spinelets, one to each of the three exposed lobes of the plate; while at the 

 end of the ray only a median spine usually persists. There is usually a single series 

 of similar dorsolateral spinelets of varying number according to size of specimen. 

 The superomarginal plates carry two or three subclavate spinelets subequal to the 

 abactinals. Usually the dorsal and exposed median, or adoral, lobe each have a 

 spinelet; sometimes the ventral lobe carries a spinelet, but less often than in S. hetero- 

 paes. The first pair of postoral adambulacral plates are in partial contact medially, 

 and the adambulacral spines are flattened and sometimes narrowly spatulate. 



The specimen from station 3885, at which the type of the species was dredged, 

 is intermediate but gives no clue to the origin of pentamerous symmetry nor to the 

 fate of the extra ray of the prevalent six-rayed young. This example, with R 18 mm., 

 differs from the fissiparous phase in having only one carinal spinelet to each plate, 

 the laterals having been absorbed. Similarly the dorsal spine of the superomarginals 

 has disappeared and only the adoral remains on each plate. The pebbled area on 

 these plates is more definitely circumscribed and that of the inferomarginals persists. 

 There is a definite and regular series of dorsolateral spines, one to a plate, and cor- 

 responding to each superomarginal spine, extending two-thirds length of ray. There 

 are two series of transverse dorsolateral connectives joining dorsolateral plates with 

 carinals and superomarginals. Straight pedicellariae on furrow margin. 



This specimen differs from the adult phase in (1) presence of spine on each cari- 

 nal and superomarginal plate, instead of on alternate plates only; (2) in the presence 

 of a well-developed series of dorsolateral spines, practically absent in adult; (3) 

 absence of circumspinal wreaths of crossed pediceUarise, these being spaced uni- 

 formly over the surface; (4) presence of "pebbling," or tiny bosses, on inferomar- 

 ginal and carinal plates (especially well marked distally). This is a feature of very 

 young specimens also. The pebbling is evidently a juvenile character which per- 



