REPORT ON THE RADIOLARIA. 729 



distal ends of the thirty-two radial spines are disposed regularly in five parallel 

 zones, and while two zones (the two j)olar) contain only the points of every four 

 spines, three zones (the single equatorial and the two tropical) contain the points of 

 every eight spines. The four meridian planes are in Actinastrum the same as in the 

 Icosacantha, crossed in the spineless axis at angles of 45°. But in the Icosacantha 

 each of the two perradial meridian planes contains six radial spines (two equatorial and 

 four polar), each of the two interradial meridian planes only four tropical spines. 

 Whereas in Actinastrum each of the two primary or perradial meridian planes contains 

 ten spines (two equatorial, four tropical, and four polar), each of the two secondary 

 or interradial meridian planes six spines (two equatorial and four tropical). We find 

 therefore altogether thirty-two radial spines in three orders ; eight equatorial, sixteen 

 tropical, and eight polar spines. 



Only one other genus of Radiolaria exhibits the same characteristic disposition 

 of thirty-two radial spines as Actinastrum, and this is Chiastolus; but here the two 

 opposite spines of each pair are grown together and form one diametral spine ; and the 

 sixteen diametral spines are crossed in the centre of the capsule. In Actinastrum, as in 

 Astrolophus and Actinelius, the central ends or bases of all the spines are pyramidal, 

 and the triangular faces of the neighbouring spines rest one upon another (as in the 

 greater number of A c a n t h o n i d a). The form of the radial spines in all Astrolophida 

 is quite simple, without lateral processes or apophyses ; chiefly cylindrical, more rarely 

 compressed, two-edged or quadrangular. 



The central capsule in all Astrolophida is si^herical, and in the j^ounger specimens 

 contains a single large concentric and lobed nucleus, but in the older specimens a large 

 number of small nuclei. The surrounding jelly-veil or calymma seems commonly to 

 envelop the spines perfectly. The piercing pseudopodia radiate everywhere between the 

 spines, and are very numerous and thin. The circulating granules in them are some- 

 times red {Actinelius purjyureus). 



Synopsis of the Genera of Astrolopliida. 



Ti T ^ ■ i-ic-i. 1 ^ c ■ i Spines of equal size, . . . 317. Adindius. 



Kadial spmes ot mdennite number and of irre- j '■ '■ ' 



° ' ' ' ( Spines of unequal size, . .318. Adroloiihun. 



Radial spines thirty -two, disposed regularly in five parallel zones, . . .319. Adinastrum. 



Genus 317. Actinelius,'^ Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364. 



Definition. — Astrolophida with a variable and undetermined number of 

 simple radial spines, all of ec[ual size, united in the centre of the spherical central capsule. 



' ^c(ineMi{S = Eadiant sun ; Uktk, ">.ioc. 

 (ZOOL. CHALL. EXP. — PAET XL. — 1885.) Rr 92 



