146 THE RADIOLARIA 



It is probable that further investigation of the Actineliida will clear 

 up the anomalies that at present attach to their isolated position. They 

 are regarded by Haeckel as the ancestral stock of the whole Radiolaria. 

 The family Litholophidae which he associated with them is now regarded 

 as composed of growth-stages of the genus A canthonia. 



FAMILY 2. ACANTHOCHIASMIDAE. With ten or sixteen diametral 

 spines irregularly arranged. Genus Acanthochiasma. With ten spines, 

 A. fusiforme, found near Plymouth and in the North Sea. A. cruciata, 

 A. krohnii, generally distributed in the Atlantic. 



SUB-ORDER 2. ACANTHONITDA. With twenty spines arranged in four 

 zones of five spines to each (Muller's Law). 



FAMILY 1. ACANTHOMETRIDAE. Spicules circular in transverse 

 section. Genera Acanthometron ; proximal end of spines without flange ; 

 A. pellucidum, N. and E. Scotland. Phyttostaurus, with flange ; Ph. 

 quadrifolius, abundant in North Atlantic. 



FAMILY 2. ZYGACANTHIDAE. Spines compressed and double-edged, 

 lanceolate in section. Genus Zygacantha, without flange at base of 

 spines ; Z. septentrionalis, North Atlantic. 



FAMILY 3. ACANTHONIIDAE. Spines cruciform in cross section. 

 Genus Acanthonia ; A. mulleri, N. Scotland and North Sea; A. 

 ligurina, W. coast of Greenland ; Acanthonidium ; A. echinoides, North 

 Sea, Faroes and Norway ; A. pallidum, N. and E. coasts of Scotland. 



FAMILY 4. AMPHILONCHIDAE. Two opposite spines much larger than 

 the rest. Genus Amphilonche. A. belonoides, generally distributed 

 in the Atlantic. For the exotic family Lithopteridae, see Haeckel's 

 Monograph (11). 



ORDER 2. Acanthophractida. 



SUB-ORDER 1. SPHAEROPHRACTA. With twenty radial spines of 

 equal size. Shell spherical. 



FAMILY 1. SPHAEROCAPSIDAE. Shell composed of very numerous 

 small plates each with a single pore. Genera 1. Sphaerocapsa. Sph. 

 cruciata, Faroes, North Atlantic*. 2. Astrocapsa. A. tritonis and A. 

 coronata, Faroes and North Atlantic. 3. Porocapsa. P. murrayana. 4. 

 Cannocapsa. C. osculata, Faroe Channel and North Atlantic. 



FAMILY 2. DORATASPIDAE. Shell composed of the meeting branches 

 of two to four apophyses given off by the twenty radial spines. Seventeen 

 genera are known, mostly from equatorial or southern waters. 



FAMILY 3. PHRACTOPELTIDAE. Shell double ; the inner one 

 enclosed by the central capsule. No genera known from northern 

 waters. 



SUB-ORDER 2. PRUNOPHRACTA. Two or six spines much larger than 

 the rest. Shell not spherical. 



FAMILY 1. BELONASPIDAE. Shell ellipsoidal. Two enlarged spines. 

 The genus Platnaspis occurs in North Atlantic and Mediterranean. 



FAMILY 2. HEXALASPIDAE. Shell lentelliptical. Six enlarged 

 spines. The genus Hexaconus is known from the North Atlantic. 



FAMILY 3. DIPLOCONIDAE. Shell diploconical with two opposite 

 large funnels (the sheaths of the two enlarged spines). Pseudopodia con- 



