Definition.—Dorataspida with twenty plates, which are perforated by eighty to two hundred or more parmal pores (in each plate two aspinal and two to ten or more coronal pores). Surface covered with by-spines.
The genus Acontaspis has the same characteristic structure of the shell as Ceriaspis, differing from it only in the presence of numerous by-spines. Each plate is perforated by four to sixteen or more (commonly ten to twelve) parmal pores, the two central of which are primary "aspinal pores," all the others being secondary "coronal pores."
Subgenus 1. Acontasparium, Haeckel.
Definition.—Plates of the shell not dimply, without prominent crests.
1. Acontaspis lanceolata, n. sp.
Shell thin walled, even, without crests and dimples between them, perforated by about three hundred pores of different sizes: forty aspinal pores elliptical, about as large as the irregular (fifty to sixty) sutural pores, and two to four times as broad as the small circular coronal pores (eight to twelve being on each plate, altogether about two hundred). Between the pores numerous short conical by-spines. Radial main spines lanceolate, about as long as the radius. (Similar to Coscinaspis peripora, Pl. [138], fig. 1, but with broad lanceolate spines and numerous short by-spines.)
Dimensions.—Diameter of the shell 0.15, aspinal and sutural pores 0.012 to 0.015, coronal pores 0.004 to 0.008.
Habitat.—South Atlantic, Station 325, surface.
Subgenus 2. Acontaspidium, Haeckel.
Definition.—Surface of the shell dimply, with a network of prominent crests.