Definition—Dorataspida without perforated plates; shell composed only of the meeting branches of the four crossed apophyses, which arise (opposite in pairs) from each radial spine. Condyles of the branch-ends bearing by-spines.
The genus Echinaspis exhibits the same structure of the shell as its ancestral form Stauraspis, and differs from it only in the development of by-spines on the sutural condyli.
1. Echinaspis dichotoma, n. sp.
Radial spines cylindrical, thin, outer half longer than the inner. Four apophyses of each spine simply forked (or partly with bifid fork-branches); therefore each spine usually possesses eight (sometimes ten to twelve) sutural condyles. Meshes of the shell ten to twelve times as broad as the bars. Each condyle bears a zigzag by-spine, half as long as the radius.
Dimensions.—Diameter of the shell 0.12, of the spines 0.004 to 0.006.
Habitat.—North Pacific, Station 253, surface.
2. Echinaspis diadema, n. sp.
Radial spines thin and long, quadrangular, prismatic; outer half two to three times as long as the inner. Four apophyses of each spine simply forked (or partly with bifid fork-branches); each spine with eight to twelve sutural condyles. Meshes of the shell fifteen to twenty-five times as broad as the bars. Each condyle bears a simple bristle-shaped by-spine, nearly as long as the radius.
Dimensions.—Diameter of the shell 0.11; breadth of the spines and bars 0.002.
Habitat.—South Atlantic, Station 333, surface.