ECHINOCYAMUS PUSILLUS. 305 



collected in Florida by Pourtales were determined in the Preliminary Report 

 as young of (Stolonoclypus) Clypeaster, basing my identification upon the 

 peculiar structure of the ambulacral area. We find that the poriferous zone 

 extends beyond the imperfect petals (PL XIII. f. 6), as a series of pores 

 in the sutures of the ambulacral plates (PL XIII. f. 2, 3), across the whole 

 width, from the base of the petals to the actinostome (PL XIII. f. 4), — a 

 character which had not previously been noticed in Echinocyamus, though it 

 was known in the flat species of Clypeaster from Midler's researches. Subse- 

 quently, however, on opening these small Echini, I found the characteristic 

 radiating partitions of Echinocyamus, while specimens of Clypeaster subde- 

 pressus showed already the concentric pillars developed near the edge of 

 test, as in PL XIII. f. 11, the small, high arched teeth of Echinocyamus also 

 greatly contrasting with the large flat teeth of Clypeaster, although at first 

 sight in these small specimens it is frequently difficult, without an internal 

 examination, to decide to which genus specimens belong, — a difficulty which 

 soon disappears when the ambulacral rosette is better developed. On com- 

 paring these specimens from Florida carefully with Norwegian specimens of 

 Echinocyamus pusillus I could detect no specific differences between them, 

 and found that E. pusillus had, like our supposed young Clypeaster, the same 

 peculiar structure of the poriferous zone. The outline varies from a pyri- 

 form to an elliptical one, more or less swollen, concave on actinal side ; the 

 pores are joined by very slight furrows ; the ambulacra three times as broad 

 as the interambulacra ; the apical system large, though not distinct; in 

 large specimens from six to seven pairs of pores to each petal. Anal sys- 

 tem small, composed of four to five triangular plates. The spines of the 

 lower part of test are more slender than those above ambitus, being fre- 

 quently subulate when exposed to much wear. The color of spines of 

 specimens when alive is greenish, frequently yellowish, or a mixture of 

 the two. 



Littoral to 325 fathoms. 



