REPORT ON THE RADIOLARIA. 599 



Suborder VI. LAECOIDEA, Haeckel, 1883 (Pis. 9, 10, 49, 50). 



Definition. — Spumellaria with lentelliptical central capsule (rarely somewhat 

 modified or allomorphic), with a lentelliptical fenestrated siliceous shell (often modified 

 or allomorphic, and sometimes quite irregular). Growth different in the three unequal 

 dimensive axes, perpendicular one to another. The typical Lentellijisis is characterised 

 by three elliptical dimensive planes of different sizes, perpendicular one to another. 



The section L a r c o i d e a, the fourth and last of the S p h se r e 1 1 a r i a, comprises 

 all those forms of this group in which the fenestrated shell originally is lentelliptical, 

 characterised by different growth in three difterent axes, perpendicular one to another, 

 all three equal on both jaoles. The geometrical fundamental form of the shell is there- 

 fore a lentellipsis or a triaxial ellipsoid ; and this typical form is preserved completely 

 in the majority of Larcoideain the pure geometrical form of the central capsule. 



The three dimensive axes, which determine the typical form of Larcoidea, are 

 commonly differentiated in such a wa}^, that the first, the longitudinal or principal axis, 

 is the longest ; both its poles, oral and aboral (or anterior and posterior) are equal. 

 The second, the lateral or transverse axis, is commonly less than the first, greater than 

 the third axis; both its poles are the equal lateral poles (right and left not difi"erentiated). 

 The third dimensive axis, the equatorial or sagittal axis, is commonly the shortest ; 

 both its ec[ual poles are the sagittal jioles (dorsal and ventral poles not different). The 

 relative size of the three dimensive axes in the human body exhibits similar relations. 



The three dimensive planes of the Larcoidea, the sagittal, lateral, and transverse 

 planes, are elliptical, all three of different sizes. The first plane, the median or sagittal 

 plane, is commonly as regards size between the two others ; its major axis is the 

 principal, its minor the sagittal axis ; it separates the right half of the body from the 

 left. The second plane or lateral plane, is commonly larger than the two others ; 

 its major axis the principal, its minor the transverse axis ; it separates the dorsal half 

 of the body from the ventral. The third plane, the equatorial or zonal plane, is 

 commonly less than the two others ; its major axis the lateral, its minor the sagittal 

 axis ; it separates the two principal halves of the body, the oral and aboral halves. 



In my Monograj)h (18G2) only very few forms of Larcoidea are described, 

 Tetrapyle and Lithelius (the latter representing a peculiar- family, Lithelida). In 

 my Prodromus (1881, pp. 463, 464) I disposed all observed forms of Larcoidea 

 in two different families, the Pylonida and Lithelida. The rich materials of the 

 Challenger collection have since offered an astonishing numl)er of new and interesting 

 forms of this section, so that I can enumerate here fifty-one genera and two 

 hundred and sixty-five sj^ecies. I dispose them here in four subsections and nine 

 families. Three of these have regular lentellijjtical shells, which are not articulate, and 



