REPORT ON THE RADIOLARIA. 491 



6. Axodiscus octogonus, n. sp. 



Eing circular or nearly octagonal, connected with the central chamber by eight radial beams at 

 nearly equal distances, which are prolonged outside into eight short conical spines. (Differs from 

 Archidisciis octoniscus in the marginal prolongation of the eight beams.) 



Dimensions. Diameter of the ring 0'04, of the central chamber O'Olo. 



Habited. Central Pacific, Station 274, depth 2750 fathoms. 



7. Axodiscus spinosus, n. sp. 



Eing circular, connected with the central chamber by ten to twelve radial beams at nearly 

 equal distances, which are prolonged outside into short conical spines of variable length. (May be 

 regarded as an aculeate variety of Archidiscus polythalamus.) 



Dimensions. Diameter of the ring 0'04 to O05, of the central chamber O014. 



Habitat. Central Pacific, Stations 265 to 274, depths 2350 to 2950 fathoms. 



Subfamily 2. TREMATODISCIDA, Haeckel, 1862, Monogr. d. Radiol., p. 491 



(sensu emendato et restricto). 



Definition. Porodiscida without radial appendages of the disk (solid spines or 

 chambered arms on the margin), and without peculiar oscula on the margin of the disk, 

 which is composed of two to four or more concentric rings. 



Genus 214. Porodiscus, 1 Haeckel, 1881, Prodromus, p. 459. 



Definition. Porodiscida with simple circular disk, composed of several rings 

 (without radial appendages or peculiar oscula on the margin of the disk). 



The genus Porodiscus is, next to its ancestral form, Archidiscus, the simplest and 

 most primitive form of the Porodiscida, from which all other genera of this family can be 

 derived. The disk is quite simple, without any marginal appendages, composed of a 

 variable number of rings, commonly of circular form, sometimes more or less polygonal, 

 elliptical, or irregular. In my Monograph (1862, pp. 491, 513) I had separated the 

 species, here united in Porodiscus, into two different genera : Trematodiscus with 

 concentric rings, and Discospira with spiral rings. But the extended study of these 

 very common forms in a great number of specimens in the Challenger collection has 

 convinced me that the separation of those two genera cannot be maintained. In 

 one and the same locality, where one single characteristic disk-form is very common, 

 we find intermingled quite regular disks with only concentric, circular rings (Tremato- 

 discus), and other disks with one single perfect spiral ring (Discospira) ; and between 



1 Porodiscus= Porous disk ; KWOS, 8iV*of. 



