REPORT ON THE RADIOLAKIA. 753 



15. Acanthonia serridata, u. sp. 



Spines quadrangular pyramidal, with simple apex ; the large basal leaf-cross nearly half as long 

 as the prolonged distal part. The four prominent triangular edges of the latter are very thin 

 and broad lamellae, finely dentate or serrate. 



Dimensions. — Length of the spines 0'2 to 0-3, greatest breadth 0-05 to O'OG. 



Habitat. — Central Pacific, Station 272, surface. 



Subgenus 3. AcanthoUthium, Ilaeckel. 



Definition. — Spine.s in the basal part grown together, so that the whole skeleton is 

 not composed of twenty separated pieces, but represents a single piece of acanthin — a 

 star with twenty equal rays. 



16. Acanthonia stellata, n. sp. 



Spines quadrangular pyramidal, with simple distal apex, in the basal part grown perfectly 

 together, so that the whole skeleton forms a single piece of acanthin — a starlet with twenty 

 equal rays. The free pyramidal part of each spine is twice to four times as long as the basal part. 



Dimensions. — Length of the spines 01 to 015, greatest breadth (on the surface of the central 

 solid sphere) 0-02 to 0-04 



Habitat. — Central Pacific, Station 271, surface. 



Subfamily 2. Phractacanthida, Haeckel. 



Definition. — A s t r o 1 o n c h i d a with twenty radial siiines, each of which bears 

 t wo opposite apophj^ses or lateral transverse processes ; sometimes two longitudinal rows 

 of opposite apophyses. 



Genus 326. Lithophylliiim ,'^ J. Miiller, 1858, Abhandl. d. k. Akad. 



d. Wiss. Berlin, p. 52. 



Definition. — A s t r o 1 o n c h i d a with two simple, not branched, opposite apophyses 

 on each radial spine. 



The genus Lithophylliuni was founded by J. Miiller for a single species (Litho- 

 phyllium foliosum), which we also here retain as the type of the genus. It is the first 

 observed Astrolonchid, which bears two opposite lateral apophyses on each spine, and 

 may therefore be regarded as the ancestral form of the subfamily Phractacanthida. The 

 two opposite apophyses are here simple, whilst in the other genera of the subfamily they 

 are branched or multiplied. 



' Lii}wphyllium = y^\ih stony leaves ; 'Ki6oi, ifvXKKi/. 



(ZOOL. CHALL. EXP. PART XL.— 1885.) Rj- 95 



