64 ECHINOIDEA. I. 



tripliyllous pedicellariae also tetradactylous pedicellariae are found. The tridentate ones occur in 2—3 

 different forms. In one form the blade is highly involuted, only the point is widened, deeply indented 

 in the edge. The second form has a shorter involuted part, and a comparatively larger widened point, 

 with coarsely sinuate edge; in the smaller specimens of this form the edge of the widened part may 

 be quite straight. (In one species (A. tesselatitvi) instead of this form a tridentate pedicellaria is found, 

 in which the edge of the blade is not at all involuted, and the blade is filled by a coarse net of 

 meshes ; in another species [A. Belli) only (?) very large specimens are found of the second form, and here 

 occurs moreover a third, smaller form with involuted edge and widened point the edges of which are 

 not sinuate. — The position of these two species is somewhat uncertain). The stalk of the pedicellariae 

 irregularly perforated. 



Species: A. fenestration (Wyv. Thorns.), coriaccnm (A. Ag.), fesselatuin (A. Ag.) (?), Belli n. sp. (?). 



Distribution: The northern Atlantic, the Viti Islands, the Philippines. — Sublittoral-archiben- 



thal forms. 



Hapalosoma n. g. 



The primary spines on the actinal side curved, with a rather long, thin hoof; they form a 

 regular, conspicuous series along the outer margins of the interambulacral areas, which series continues 

 some way up on the abactinal side. The areoles not very large; no conspicuous difference between 

 the actinal and the abactinal sides. The tube feet in three series — almost as in an Echinus. The 

 spicules almost rod-shaped, above somewhat larger fenestrated plates, arranged in two series; the 

 sucking disk well developed. Three kinds of pedicellariae: globiferous, tridentate, and triphyilous ones. 

 In the globiferous ones the glandular bags are quite wrapped in a common skin; they open in the 

 point of the head each through a separate little pore. The valves, which are situated between the 

 glandular bags, reach only half-way to the point. The tridentate pedicellariae are simply leaf-shaped, 

 with an only slightly developed net of meshes; only this form is found. The stalk of the common 

 structure. 



Species: H. pellucidum (A. Ag.). 



Distribution: The Philippines, New Guinea. — Sublittoral form. 



Hygrosoma n. g. 



The primary spines on the actinal side curved, with a large, white hoof; they are scattered 

 near the ambitus; the areoles large; the difference between the actinal and the abactinal sides rather 

 great. The tube feet are arranged in one almost regular series on the actinal side. The spicules 

 large fenestrated plates, no sucking disk. Only tridentate and triphyilous pedicellariae. The tridentate 

 ones occur only in one form, highly involuted; the point is widened in a spoon-like manner, and its 

 edge is straight. The stalk of the pedicellariae of the common structure. Iu one species, H. lucu- 

 lentum, another kind of tridentate pedicellariae is found, with very thick and broad blades, almost as 

 ophicephalous pedicellariae ; but the species cannot with certainty be referred here. 



Species: H. Petcrsii (A. Agass.), hoplacantha (Wyv. Thorns.), luculentum (A. Ag.) (?). 



Distribution: The northern Atlantic, the Pacific. — Sublittoral-archibenthal forms. 



Tromikosoma n. g. 

 The primary spines on the actinal side curved, with a large hoof, they are only few and 



