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



1. Astrolophus stellaris, u. sp. 



Iladial spines from one hundred to two hundred, of very different sizes, but of similar form ; 

 about sixteen to twenty very large spines, forty to fifty of medium size, and one hundred to one 

 hundred and twenty much smaller. All spines cylindrical in the gi-eater part of their length, with 

 simple apex, gradually thickened towards the central part, conical, without edges. The base itself 

 is a slender pyramid with four to eight edges. 



Dimensions. — Length of the largest spines 0"3 to 04, of the majority 01 to 0-2, of the 

 smallest 0'05 to 01. 



Habitat. — South Pacific, Station 288, surface. 



2. Astrolophus Solaris, n. sp. (PL 132, figs. 12a, 12^). 



Eadial spines from two hundred to three hundred, of very different sizes, but of similar form ; 

 about twenty to thirty very large spines, sixty to eighty of medium size, and one hundred and twenty 

 to one hundred and fifty much smaller. All spines cylindrical in the greater part of their length, 

 with simple apex, gradually thickened and. four-edged towards the central Ixise. The base itself is a 

 slender pyramid with four to eight edges ; partly the faces, partly the edges of these basal pyramids 

 rest one upon another, the points of the larger spines meeting in the centre. 



Dimensions. — Length of the largest spines O'l to 0-5, of the majority 0-2 to 0-3, of the 

 smallest 01 to 016; basal thickness of the largest spines O'Olo. 



Habitat. — South-east Pacific (off Juan Fernandez), Station 296, surface. 



Genus 319. Actinastrum,^ n. gen. 



Definition. — A s t r o 1 o p li i d a with thirty-two simple radial spines, regularly 

 disposed vi^ithin four meridian planes in such an order that their distal ends fall into 

 five parallel zones. Central ends of the thirty-two spines supported one upon another 

 in the centre of the spherical central capsule. 



The genus Actinastrum differs from the two preceding genera iu the definite 

 number and order of the thirty-two radial spines, which are disposed in a very 

 remarkable manner. Twenty radial spines are disposed after the Miillerian law of 

 Icosacantha (compare above, p. 717). The remaining twelve spines are four equatorial 

 spines Ij^ing in the two secondary meridian planes, and eight tropical s^jines lying in 

 the two primary meridian planes. We have therefore together eight equatorial, sixteen 

 tropical, and eight polar spines (compare above, p. 729). 



' .dciijiosintm = Radiant star; oixTiV, slaT^on. 



