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



without ring and dimple. Four edges of the spines. smooth ; their length scarcely equals half the 

 shell-radius. 



Dimensions. Diameter of the shell 015 ; length of the spines 0'03, of the tubuli O08. 



Habitat. South Atlantic (east coast of Patagonia), Station 318, surface. 



Subfamily 3. CENOCAPSIDA, Haeckel. 



Definition. Kadial spines completely reduced and absent; shell cavity there- 

 fore simple ; shell pierced by twenty perspinal pores (each placed in the direction of one 

 radial spine which has disappeared). 



Genus 348. Cenocapsa, 1 n. gen. 



Definition. S phserocapsida without radial spines, with simple cavity of the 

 spherical shell, which is pierced by twenty perspinal holes (each one placed in the radial 

 direction of one spine which has disappeared). 



The genus Cenocapsa comprises only a single species, but is very remarkable in 

 that it is the most reduced form among all Sphaerocapsida. The twenty radial spines of 

 the Icosacantha have perfectly disappeared by complete retrograde metamorphosis, and 

 the only evidence of their, former existence (in the ancestral genus Porocapsa) are 

 the twenty perspinal holes remaining in the shell. Cenocapsa is the only form of 

 ACANTHARIA which possesses no radial spines. 



1. Cenocapsa nirvana, n. sp. (133, fig. 11, lla). 



Perspinal holes four-lobed, cruciform, with four short triangular teeth between the four lobes of 

 the cross. Poruli of the shell in the bottom of an elliptical dimple surrounded by an elevated ring. 

 Dimensions. Diameter of the shell O2 to 0'3, of the aspinal holes 0'02. 

 Habitat. North Pacific, Station 248, surface. 



Family XL. D OR AT AS PID A, Haeckel (Pis. 134r-138). 



Dorataspida, Haeckel, 1862, Monogr. d. Eadiol., p. 412. 



Definition. ACANTHARIA with simple spherical lattice-shell, composed of the 

 branched apophyses of twenty equal radial spines meeting in its centre and disposed 

 according to the Miillerian law of Icosacantha. Central capsule spherical, enclosed in 

 the fenestrated shell. 



The family Dorataspida is the most important family of the Acantho- 

 phracta, or of those ACANTHARIA in which the radial spines are connected by a 

 complete extracapsular lattice-shell. The Dorataspida represent probably the ancestral 



1 Cenora]'fa='Ro\\ovf capsule ; xti/es, *^*- 



