REPORT ON THE RADIOLARIA. 893 



trace of a sagittal ring nor of a basal tripod. This is the case in the remarkable family 

 of Cyrtocalpida (Archicorida and Ai'chicapsida), in numerous Botryodea and in other 

 C y r t e 1 1 a r i a. 



D. The skeleton is composed of a sagittal ring and a basal tripod, without latticed 

 cephalis. This is the case in a few, but very important forms of Stephoidea: 

 Cortina, Stephanium, Cortiniscus, Stephaniscus, Podocoronis, and some allied genera. 



E. The skeleton is composed of a sagittal ring and a latticed cephalis, but without 

 basal tripod. This is the case in numerous Cyrtellaria, in the Circospyrida (or 

 Zygospyrida apoda: Dictyospyris, Circospyris) and some other Spyroidea; and in 

 a large number of Botryodea and Cyrtoidea eradiata (a part of the Sethocyrtida, 

 Theocyrtida, Lithocampida, and others). 



F. The shell is composed of a basal tripod and a latticed cephalis, but without any 

 trace of the sagittal ring. This is the case in numerous Cyrtoidea trii'adiata and 

 multii-adiata, and perhaps in the majority of the following families — Tripocalpida, 

 Tripocyrtida, Podocyrtida, and Podocampida. 



G. The shell is composed of all three above-mentioned elements, of a sagittal ring, a 

 basal tripod, and a latticed cephalis. This is the case in the great majority of Spyroidea 

 (with a few exceptions only), and perhaps also in the majority of Cyrtoidea. 



The survey of these seven groups, A to G, each of which is represented by 

 numerous living forms, shows clearly how difficult and complicated the morphology 

 and phylogeny of the numerous Nassellaeia must be. For all possible combinations 

 of the three original structural elements are realised abundantly, and in such compli- 

 cated relations, and so intermiua;led in the different orders and families, that it seems 

 nearly hopeless to answer the question of theii- true origin. The identity in the 

 structure of the central capsule, however, in all these Monopylea, makes it probable 

 that they have all arisen originally from the skeletonless Nassellida (Cystidium, 

 Nassella), either in a monophyletic or in a polyphyletic w^ay. In this respect the 

 following phylogenetical hypotheses are possible. 



1. Monophyletic hypothesis, deriving all Nassellaeia from a simple sagittal ring 

 {Archicircus, Lithocircus, &c., PL 81). The groups A, D, E, and G may be derived 

 easily from such a ring, but the groups B, C, and F only by means of the hypothesis 

 that the original ring may be completely reduced and finally lost. This hypothesis 

 was stated by me in the years 1877 to 1879, when I had got the first general survey of 

 the astonishing number of new Nassellaeia in the Challenger collection, and as I had 

 found the sagittal ring in the majority of them. This, my former hypothesis, is mentioned 

 by Ptichard Hertmg (1879, loc. cit., pp. 68, 126). It was afterwards supported wdth 

 particular energy by 0. Bhtschli (1882, Zeitschr. fiir wiss. Zool., Bd. XXXVL). 



2. ]\lonophyletic hypothesis, deriving all Nassellaeia from a basal tripod 

 {Triplagia, Plagoniscus, &c., PI. 91). The groups B, D, F, and G, all trii-adiate, may 



