ART. 5 ECHINODERMS FROM THE TONGA ARCHIPELAGO — CLARK 3 



Family ECHINIDAE 



TRIPNEUSTES GRATILLA (Linnaeus) 



Two specimens, one with dark and the other with whitish spines. 

 Family ECHINOMETRIDAE 



PARASALENIA GRATIOSA A. Agassiz 



Nukualofa Island. Two specimens; the larger is parasitized by a 

 small gastropod. 



The larger specimen measures 33 mm. in the longer axis and 26 

 mm. in the shorter. The longest spines on the longer axis are 23 mm. 

 in length, and the longest spines on the shorter axis measure 19 mm. 



The periproct is largely covered by five large plates. Of these, 

 two are situated on the inner border of genital 1, one is on genital 2, 

 one occupies the whole inner edge of genital 3 and about two-thirds 

 of that of genital 4, and one occupies one-third of the inner border of 

 genital 4 and nearly all that of genital 5. These plates are short 

 with broadly rounded tips, and the center of the periproct is covered 

 with eight small subequal plates. 



Genital 3, though long, is very narrow, and its inner border is 

 only about half as long as that of genitals 2 and 4. Genital 1 is 

 short but broad, and genital 5 is the smallest, triangular, with its 

 inner border about twice as long as that of the elongate rhombic 

 genital 3. 



Genitals 4, 5, and 1 each bear a single cylindrical or more or less 

 club-shaped spine 2 mm. long situated near the inner edge. Genital 

 2 bears two spines, one diagonally behind and close to the other. 

 Genital 3 bears two spines, one in the middle of the plate and one 

 near the inner border. In addition to these spines, the genitals bear 

 a few pediceilariae, some of which have jointed stalks. 



Oculars II and V are insert, and ocular I is very nearly so, but 

 oculars III and IV are very widely excluded from the periproct. 

 Oculars II, III, and IV each bear a spine similar to the spines borne 

 by the genitals. 



Most of the spines remain cylindrical from the base to the end of 

 the proximal third or half, from that point tapering regularly to 

 the tip, but some taper regularly from the base, and some increase 

 slightly in diameter as far as the end of the proximal third or half. 



The test is deep black. The spines are dark olive-brown, most of 

 them with the tips polished. The spines at and below the ambitus 

 are somewhat lighter with longer and more prominent polished tips. 

 The milled ring is pure white and very conspicuous. 



