REPOET ON THE EADIOLARIA. 935 



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 or elliptical, or more polygonal, and is connected with the basal rod of the sagittal 

 ring by three paii'S of radial apophyses, the anterior furcular, the middle coracal, and the 

 posterior scapular rods. 



A thiixl important form of Semantida is Semantidium (PI. 92, figs. 6, 7). Here 

 we find three pairs of basal j3ores in the seal-plate ; the third pair, newly formed, 

 consists of the cervical gates (e), bounded in front by the scapular rods {d), 

 behind by a fourth pair of basal apophyses, the cervical rods. 



The basal apophyses of the sagittal ring are not only of great morphological 

 importance, because they produce by their union three typical pairs of basal gates or 

 " collar pores," but also because their prolongations often appear as typical basal feet. 

 The distal prolongations of the coracal rods appear in Semantiscus (PI. 92, figs. 16—18) 

 as two pectoral feet, those of the scapular rods as two tergal feet, whilst the opposite 

 prolongations of the basal rod of the sagittal ring appear as two " sagittal feet " (in front 

 an anterior or sternal, and behind a posterior or caudal foot). In the typical Cortiniscus 

 (PI. 92, figs. 11-13) only three feet are developed; an odd caudal and two paired 

 pectoral feet (compare above, p. 891). The typicah basal ring of the Semantida, with its 

 paired basal gates (Seinantis), reappears in the majority of the Coronida, differing from 

 the former in the development of a second vertical ring, which lies in the frontal plane 

 (perpendicular to the sagittal ring), and which we therefore call the frontal ring. In only 

 one small group of the Coronida the basal ring is absent, namely, in the Zygostephanida, 

 and here the frontal ring appears in the simplest form, as a complete elliptical meridian 

 ring, crossing the sagittal ring perpendicularly on the two poles of the main axis 

 (^Zygostejjhanus, PI. 93, figs. 1—4). Four large lateral gates between the two rings 

 remain open. This form may be derived directly irom. the Stephanida in the following 

 way; fr'om both poles of a simple sagittal ring there arise two opposite lateral apophyses, 

 which in the frontal plane become curved one towards the other, and united in the poles 

 of the transverse axis. The basal apophyses would be the coracal rods. But it is also 

 possible that Zygostephanus was derived from Semantis by the loss of the furcular rods. 



The three typical rings (or the " dimensive rings ") of the Stephoidea appear 

 in their most complete form in the subfamily Trissocyclida (PI. 93, figs. 7, 13). 

 Here all three rings are undivided and completely developed in the three dimensive 

 planes, perpendicular one to another. Between them there remain eight large open 

 gates ; the four superior are the four " lateral gates " of Zygostephanus, the four 

 inferior are the four basal gates of Semantrum. The four latter are originally much 

 smaller than the four former; but in Trissocircus and Trissocyclus (PI. 93, figs. 10—12) 

 they reach the same size. Therefore all eight gates are here of equal form and similar 

 size, and the basal ring, now a true equatorial ring, divides the two meridional rings 

 into two equal halves. 



In the Eucoronida, a thuxl subfamily of Coronida, the sagittal and the basal rings 



