REPORT ON THE RADIOLARIA. CXXl 



(p. 950, § 182). The Stephauida are the most archaic family among the Stephoidea 

 (p. 937, PL 81), perhaps indeed among all the Nassellaria (§ 184); in them the 

 sagittal ring and its processes alone constitute the skeleton ; secondary rings and meshes 

 are wanting. Two diverging families, the Semantida and Coronida, have been developed 

 from the Stephanida, and from one of them the family Tympanida has arisen. 



The Semantida (p. 953, PI. 92) develop a horizontal basal ring at the oral side of the vertical 

 sagittal ring ; the basal meshes or lattice gates, which remain between the former and the latter, 

 are the important cortinar pores (one pair jugular, one pair cardinal, p. 954); they usually appear 

 inherited in the cortinar septum of the C y r t e 1 1 a r i a. In the Coronida (p. 967, Pis. 82, 94) a 

 second vertical ring (the frontal ring) appears in addition to the sagittal ring ; it lies in the frontal 

 plane at right angles to the latter. Finally the Tympanida (p. 987, Pis. 93, 94) have probably 

 arisen from the Semantida by the formation of a second horizontal ring (mitral ring) parallel to 

 the basal and attached to the upper portion of the sagittal ring. 



188. Genealogical Tree of the Spyroidea. — The extensive order Spyroidea is 

 of especial interest in connection with the phylogeny of the Nassellaria, since all its 

 members show two well-developed skeletal elements in combination, the sagittal ring of 

 the Stephoidea and the latticed cephalis of the C y r t o i d e a; the majority possess 

 also the basal tripod of the P 1 e c t o i d e a (or a radial skeleton derived from it). Hence 

 there is a possibility of deriving the stem -forms of the Spyroidea from each of these 

 three groups. The four families of this order exhibit similar relationships to those of 

 the four families of C y r t o i d e a ; the common stem-group is the family Zygosppida ; 

 from this the Tholospyrida have arisen by the development of a galea on the apical 

 pole, the Phormospyrida by the addition of a thorax on the basal pole. The Andro- 

 spyrida may be derived either from the Tholospyrida by the formation of a basal 

 thorax, or from the Phormospyrida by the development of an apical galea. Some 

 groups, however, such as the peculiar Nephrospyrida (PL 90) have probably been 

 developed directly from the Stephoidea. 



189. Genealogical Tree of the Botryodea. — The peculiar order Botryodea 

 (p. 1103), which is both difficult to investigate and insufficiently known, presents great 

 phylogenetic difficulties both as to its ascent and descent. Probably the different 

 genera of this order have been polyphyleticaUy developed from different groups of 

 Cyrtoidea (perhaps also to some extent of S p y r o i d e a) by the formation of lobes 

 in the cephalis. The three families of Botryodea are related to each other in the 

 same way as are the three first families of the Cyrtoidea. From the single-jointed 

 Cannobotryida (corresponding to the Monocyrtida), the two-jointed Lithobotryida 

 (corresponding to the Dicyrtida), may be derived by the development of a basal 

 thorax, and from the latter the three-jointed Pylobotryida (like the Tricyrtida) by the 

 addition of an abdomen. In the last two families the forms with an open basal mouth 



(ZOOL. CHALL. EXP. — PART XL. — 1886.) Rr q 



