REPORT ON THE RADIOLARIA. 939 



nearly always polygonal, with prominent corners, and usually from these arise thorns 

 or branched spines which are regularly disposed. Eegardiug this disposition we may 

 distinguish three cases : A, the spines lie in the sagittal plane and form a single row, 

 arising from the median edge ; B, the spines lie on both sides of the latter and form 

 two parallel rows, arising from the two lateral edges ; C, the spines represent a com- 

 bination of A and B, and are disposed in three rows, two paired rows arising from the 

 two lateral edges, and an odd middle row between them, arising from the median edge. 

 The spines are simple, without branches, in Archicircus and Zygocircus ; more or less 

 branched in Lithocircus and Dendrocircus. The branches are often richly ramified 

 or arborescent, and exhibit great variety in size, special form, and direction (compare 

 PI. 81). 



The number and disposition of the spines or groups of spines are usually constant, 

 and may be employed in the further progress of our knowledge, to distinguish a number of 

 genera and subgenera. Very commonly (perhaps in the majority of the Stephanida) we 

 find six groups of spines, an apical group on the upper rod of the sagittal ring, a basal 

 group on the lower rod (on the porochora of the central cajDsule), two ventral groups on 

 the anterior rod, and two dorsal groups on the posterior rod. In other species we find 

 four or eight groups instead of six, and sometimes a larger number. 



The most important of these apophyses of the ring are the basal spines, arising 

 from its basal pole, where the porochora of the central capsule rests upon it. 

 They are often much larger and more branched than the other spines, and attain a 

 peculiar morphological value in the small subfamily Cortinida. Here we find three 

 or four regularly disposed " basal spines," which may be compared to the typical " basal 

 feet" of the Cyrtellaria, appearing in the majority of Spyroideaand 

 Cyrtoidea. Cortina, one of the most important Nassellaria, bears three typical 

 divergent feet on the base of the simple ring, two paired anterior or " pectoral feet," 

 and an odd posterior or " caudal foot." The latter appears as a direct basal prolonga- 

 tion of the dorsal rod of the ring, and is opposed to an upper prolongation of the same, 

 which corresponds to the "apical horn" of the Cyrtellaria (PL 97, figs. 1-3). 

 As already explained above, these three basal feet of Cortina possess the highest phylo- 

 genetic value, since they may also be compared with the three primary radial spines of 

 the Plectoidea, and so connect the Cyrtellaria and the Plectellaria. 

 Stephaniiim di9"ers from Cortina in the possession of four basal feet, an odd anterior or 

 " sternal foot" being added to the three typical feet of the latter (PI. 92, figs. 20, 21). 

 Some forms of Plectoidea (Plagoniscus, Plectaniscus, &c.) seem to be nearly 

 related to these Cortinida, and may be easily transformed into them by development 

 of a complete ring, embracing the central capsule. They seem to demonstrate the near 

 affinity of all these triradiate Nassellakia (PI. 91, figs. 4, 5, 9, lO). 



