834 THE VOYAGE OF H.M.S. CHALLENGER. 



2. Zonaspis cingulata, n. sp. (PL 134, figs. 3, 4). 



Eadial spines cyliudrical iu the inner half, with thickened pyramidal bases (fig. 3), conical in 

 the outer half ; both halves of equal length. The four meshes of each equatorial plate egg-shaped, 

 four to six times as broad as the bars. By-spines zigzag, half as long as the radius. 



Ditnensians. — ^Diameter of the shell 0"15, of the parmal meshes 0'015. 



Hahitat. — Tropical Pacific (east coast off Philippines), Station 275, surface. 



3. Zonaspis (equator led is, n. sp. (PL 135, fig. 5). 



Eadial spines stout, cylindrical in the shorter inner half, conical in the longer outer half. The 

 four meshes of each equatorial plate circular, only twice as broad as the bars. By-spines zig- 

 zag, nearly as long as the radius. 



Dimensions. — Diameter of the shell OH, of the parmal meshes O'OOS. 



Habitat. — ^Equatorial Atlantic, Station 347, surface. 



Genus 361. Dodecaspis,^ n. gen. 



Definition. — D o r a t a s p i d a with twelve plates, each of which is jjerforated by 

 four crossed aspinal pores ; these twelve plates are formed by the united branches of 

 the apophyses of four equatorial and eight j)olar spines. The branches of the apophyses 

 of the eight troj)ical spines form no lattice -plates by union. Each condyle bears a 

 by-spine. 



The genus Dodecaspis differs from all other Dorataspida in the peculiar composition 

 of its shell ; twelve spines (four equatorial and eight polar spines) form by union of 

 the branches of their apophyses twelve plates, each of which exhibits four crossed pores, 

 whilst the eight other (tropical) spines form no perforated plates, but simply unite with 

 the neighbouring spines by meeting branches. Some irregularity is often to be found 

 in this genus ; instead of four pores in each plate there may be two closed, the other 

 two which are opjiosite being open. Several times I observed a peculiar " hemihedral " 

 variety : only six spines of one meridian plane (the two equatorial and the four 

 polar spines of the " hydi'otomical " plane) exhibited complete shields, whilst the 

 branches of the other fourteen plates remained open. This " hemihedi'al ".form may 

 perhaps represent a peculiar genus, Heniiaspis. 



1. Dodecaspis iricinata, n. sp. (PI. 134, fig. 1). 



Eadial spines thin and long, cyliudrical. The four meshes of each eqiiatorial and each polar 

 plate of equal size, pentagonal, about eight times as broad as the bars. By-spines zigzag, 

 nearly as long as the radius. In this species the hemihedral variety, Hcmiaspis, often occurs. 



JDimensions. — Diameter of the shell 015, of the parmal pores 016. 



Hahitat. — South-east Pacific (west coast of Patagonia), Station 302, surface. 

 ' Dodecasj.is = Shell with twelve shields ; IuZskk, davi's. 



