862 THE VOYAGE OF H.M.S. CHALLENGEE. 



Genus 371. Thoracaspis,^ Haeckel, 1862, Prodromus, p. 468. 



Definition. — B e 1 o n a s p i d a witli forty parmal pores (two on eaeli plate), without 

 dimples and crests, also without by-spiaes, therefore with smooth surface. 



The genus Thoracasiyis is the simplest form among the Belonaspida, and repeats in 

 this family the nearly allied genus Dorataspis among the Dorataspida. It differs from 

 this genus only in the characteristic prolongation of one equatorial axis, which effects an 

 ellipsoidal transformation of the spherical central capsule and the enclosing lattice-shell. 



1. Tlioracaspis eUipsoides, n. sp. 



Parmal pores large, elliptical, five or six times as large as the small circular sutural pores. Eacli 

 plate surrounded by five or six sutural pores (a single one on each side). Spines compressed trian- 

 gular, sword-like, two-edged ; inner and outer half of nearly equal length. 



Bimcnsions. — Length of the ellipsoidal shell (or major axis) 015, breadth (or minor axis) 0-12 ; 

 length of the spines 0'07, basal breadth 0'016. 



Habitat. — North I'acific, Station 253, surface. 



2. Thoracasjns ■nephwjwra, n. sp. 



Parmal pores large, kidney-shaped, three to four times as large as the roundish small sutural 

 pores. Each plate surrounded by five or six sutural pores (a single one on each side). Spines in the 

 inner longer part cylindrical, in the outer shorter part conical, not compressed. 



Bi'iiiensions. — Length of the shell 0'2, breadth 015 ; length of the spines O'OG, basal breadth 

 0-018. 



Hahitat. — Central Pacific, Station 268, surface. 



3. Tlioracaspis circopora, n. sp. 



Parmal pores circular, of the same size as the circular sutural pores. Each plate surrounded 

 by five or six sutural pores (a single one on each side). Sjiines compressed, thin, linear, two-edged ; 

 outer part one and a half times as long as the inner. 



Bimcnsions. —'L&ugih. of the .shell 017, breadth 013; length of the spines 012, basal breadth 

 0-003. 



Habitat. — South Pacific, Station 288, surface. 



4. Thoracasp>is hipennis, n. a^. (PI. 139, fig. 8). 



Parmal pores elliptical, about twice as large as the circular sutural pores, which are of rather 

 variable size. Each plate surrounded by eight to twelve sutural pores (commonly two on each side). 



' r/ioracospis = Cuirass-shielil; Ui^a^,aa7r's. 



