SPECIAL MORPHOLOGY AND TAXONOMY OF SARCODINA 347 



Family 1. Acantharidse, Haeckel. —Forms with 20 spines arranged 

 according to the Miillerian law and all of approximately the same 

 length {Acanthometra elasHca). 



Family 2. Sphserophractidse, Haeckel.— Forms with 20 spines of 

 equal length arranged as abo\e; each spine with outgrowths from 

 one or more places. These outgrowths are equally distant from 

 the center and may fuse, forming one, two or more concentric shells 

 or skeletons (SjjhcBrocapsa, Haeckel). 



Family -3. Prunophractidse, Haeckel.- Forms similar to the above 

 but with spines of imequal length resulting in correspondingly 

 characteristic changes in the central capsule, skeleton, and axial 

 relations. ( Tlwracaajyis, Haeckel) . 



Family 4. Actinellidae, Haeckel.— In this group the spines are 

 more than 20 in number; Haeckel held that they are in midtijjles of 

 20, and he regarded this family as the most primitive of the Acan- 

 tharia. {Actinelius, Haeckel, Podactinelius, Schroder, Litholophiis, 

 Haeckel). 



Okder hi. MONOPYLEA, Hertwig. 



The Radiolaria included in this Order are richly represented 

 amongst fossil and recent types. They differ from all others in 

 having a central capsule with its openings confined to one pole. 

 The pores are in a portion of the central capsule membrane which 

 forms the base of a conical volume of endoplasm, the podoconus, the 

 apex of which is in the center of the endoplasm. The form of the 

 central capsule is frequently fantastic, or radial, or bilaterally sym- 

 metrical. The nucleus is single, elongate and excentric in position. 



The skeleton is invariably silicious and may be developed in a 

 multitude of different forms based upon modifications of three 

 parts, the basal spines, the "head" or capitulum, and the ring. 

 These may be independent, or connected by fused spines, etc., with 

 the tendency to form latticed skeletons which furnish the basis for 

 the other name— Nassellaria— first used by Ehrenberg and amended 

 by Haeckel to include forms in this Order. 



Family 1. Nassoidae, Haeckel.— Monopylea without skeletons. 



Family 2. Plectoidae, Haeckel. —Forms without capituhnn or ring, 

 but with basal s])ines which are frequently branched. 



Family 3. Stephoidae, Haeckel.— Invariably with a simple or 

 multiple ring })ut without capitulum or basal spines. 



Family 4. Cyrtoidse, Haeckel.— With a well developed capitulum 

 which is attached to the basal spines but without ring. 



Family 5. Spyroidse, Ehrenberg. —Here the well developed capitu- 

 lum is divided by a sagittal cleft into two halves; basal spines also 

 present. 



Family (i. Botryoidse, Haeckel.— Forms similar to those of the 

 last family but without basal spines and with a mantle-like lengthen- 

 ing of the capitulum. 



