REPORT ON THE RADIOLARIA. 697 



Subgenus 2. Larcospironium, Haeckel. 



Definition. Spiral convolutions or turns of the cortical shell double; both wings 

 of the transverse girdle turning around the principal axis. 



4. Larcospira oliva, n. sp. 



Cortical shell with smooth surface, six times as long as the lentelliptical medullary shell. 

 Perimeter of the lateral plane elliptical, one and a fourth times as long as broad, without 

 constrictions. Both lateral wings of the transverse girdle turn round one another and form one and 

 a half to two double spiral turns. 



Dimensions. Length of the cortical shell 0'25, breadth 0'2 ; length of the medullary shell 0'04, 

 breadth 0'035. 



Habitat. Antarctic Ocean, Station 157, depth 1950 fathoms. 



Genus 307. Pylospira, 1 n. gen. 



Definition L ithelida with double, trizonal or Larnacilla-sha.'ped medullary shell ; 

 cortical shell subspherical or lentelliptical, constructed of a single or double spiral of the 

 lateral girdle (or second cortical girdle) ; the spiral lamella revolving round the sagittal 

 axis. 



The genus Pylospira follows after Larcospira as the second genus of Larcospirida ; 

 but in this latter the spiral of the cortical shell is formed by the transverse girdle (or the 

 first lattice-girdle of the Diplozonaria), whilst in Pylospira it is produced by the lateral 

 girdle, or the second lattice-girdle of that group. Therefore Pylospira may be derived 

 phylogenetically from Tetrapyle in the same manner as Larcospira from Amphipyle. 

 Whilst in this latter the first cause of the spiral turning, the unequal growth of both 

 girdle-wings, proceeds from the transverse girdle, in Pylospira it proceeds from the 

 lateral girdle. One of its wings overgrows the other, turning around the sagittal axis. 

 If the second wing do not become developed, the spiral remains simple and represents 

 the subgenus Pylospirema; but if afterwards the second wing follow the example of the 

 first and overgrow it from the other side, we reach the typical form of the second 

 subgenus, Pylospironium, with a double spiral. 



Subgenus 1. Pylospirema, Haeckel. 



Definition. Spiral convolutions or turns of the cortical shell simple, only one 

 single wing of the lateral girdle turning around the sagittal axis. 



1 Pylo>ipira = Spiral shell with internal gates ; xv^n, amiga. 

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