EEPORT ON THE RADIOLARIA. 



■41 



circular, in the second ellii3tical or lanceolate, in the third square. All the different forms 

 of spines, which we find in the numerous Acanthaeia, may be reduced to these three 

 forms, and among these the second and third are "derived from the first. 



The development of apophyses or of lateral transverse processes (wanting in the 

 Zygacanthida) is of the greatest value for the further difi'erentiation of the AcANTHAPaA. 

 For from the Phractacanthida (with two opjiosite apophyses on each spine) we must 

 derive the Phrastaspida, the common ancestral stock of the Diporaspida (and therefore 

 also the Belonaspida, Hexalaspida, Diploconida, and Phractopeltida). On the other hand 

 the Stauracanthida (with four crossed apophyses on each spine) have produced the 

 Stauraspida, or the ancestral group of the Tessaraspida and Sphserocapsida. From 

 all these A c a n t h o p h r a c t a, possessing a complete lattice-shell, the Astrolonchida 

 difier in the absence of such a complete shell. Also in the few cases in which the 

 apophyses become latticed (Doracantha among the Phractacanthida, and Phatnacantha 

 among the Stauracanthida), the lattice-plates of the neighbouring spines never 

 meet with their edges, as is the case in all A can t hop hr act a. But in a phylo- 

 genetic as well as in an ontogenetic sense the former are the ancestral stock of the latter. 



The Central Capsule in the Astrolonchida is commonly spherical, sometimes with 

 twenty roundish elevations or conical papillae, extending radially to the basal half of the 

 radial spines. The calymma is voluminous, and forms around the radial spines conical or 

 cylindrical "jelly-sheaths," which are connected with the spines by coronas of Myophrisca 

 (or of the bodies formerly called " Gallert-cilien," afterwards recognised as " contractile 

 Filamente "). 



Synopsis of the Geneva of Astrolonchida. 



Spines cylindrical, with circular transverse section, 



I. SulDfamily 



Zygacanthida. 

 Twentyradialspines simple, 

 without apopliyses or 

 lateral transverse pro- 

 cesses. 



II. Subfamily 



Phractacanthida. 

 Twenty radial spines pro- 

 vided each with two 

 opposite apophy.ses (or 

 two longitudinal rows of 

 apophyses). 



III. Subfamily 



Stauracanthida. 



Twenty radial spines pro- 

 vided each with four - 

 crossed apophyses (or 

 four crossed longitudinal 

 rows of apophyses). 



Spines compressed, two-edged or lamellar, with elliptical 

 or rhomboidal transverse section, 



Spines quadrangular (prismatic or pyramidal), with four 

 edges, with square transverse section, . 



Two apophyses opposite on 

 each spine. 



Apophyses simple. 

 Apophyses branched, 



Apophyses latticed, 



Two opposite longitudinal rows of apopliyses (four to 

 eight or more apophyses on each spine, opposite in 

 pnirs), . . . . ■ . 



f Apophyses simple. 

 Four apophyses (in cross I 



form) opposite in pairs \ Apophyses branched, 

 on each spine. 



[ Apophyses latticed. 



Four longitudinal rows of apophyses, opposite in pairs in 

 cross form on each spine, .... 



3'2.3. Acanthnmi'trnn. 



324. Zijgacantlia. 



325. Acanthoma. 

 32G. Lithophjllium. 



327. Plivadacantha. 



328. Doracantha. 



329. Admlonche. 



330. Xipliacantha. 



331. Stauracantha. 



332. Phatnacantha. 



333. Pristaeantha. 



