606 



THE VOYAGE OF H.M.S. CHALLENGER. 



most simple forms of all L a r c o i d e a, we can regard the Cenolarcus as the common 

 ancestral form of this group, having originated from Actolarcus (or the lentelliptical 

 Actissa) by the building of a simple lentelliptical lattice-shell. But it is also possible 

 that a part of the Larcarida (or all ?) descend from Larnacida by reduction or loss of the 

 original La^^nacilla-shell (compare Cenolarcus triaxonius, p. 607). 



Sy7iopsis of the Genera of the Larcarida. 



I "Without radial spines, 



I 

 r 



J 



I. Subfamily 



Cenolarcida. 

 SheU simple, latticed (lentelliptical cortical \^ ^^,.^j^ ^,^^^^ .^^^^ 

 shell). ' 



II. Subfamily 



Coccolarcida. 

 Shell composed of two or more concentric ' 

 latticed shells (inner medullary and outer 

 cortical). 



Without radial spines, 



III. Subfamily 



Spongolarcida. 

 SheU spongy, partly or whole composed of a f y^j-^^^^^^^ ^^^ i^t^.^^^l ^^^it 

 sponKv framework. 



With radial spines, 



I With an internal cavity, 



I 



r 

 J 



266. Cenolarnis. 



267. Larcariuin. 



268. Coccolarcus. 



269. Larcidium. 



270. Spongolarcus. 



271. Stypolarcus. 



Subfamily 1. Cenolaecida, Haeckel. 



Definition. — Larcarida with simple, lentelliptical latticed shell (cortical shell 

 without a medullary shell). 



Genus 266. Cenolarcus,^ n. gen. 



Definition. — Larcarida with a simple, lentelliptical latticed shell, without a 

 medullary shell, without radial spines. 



The genus Cenolarcus begins the group of L a r c o i d e a as the most simple form 

 of this suborder. It corresponds to Cenosphcera among the Sphseroidea, to Ceno- 

 discus among the D i s c o i d e a, to Cenellipsis among the P r u n o i d e a. The simple 

 latticed shell is distinguished from that of the three other genera by its typical 

 lentellijjtical form, a triaxial ellipsoid with three dimensive axes of unequal length. 

 Probably Cenolarcus is the original ancestral form of the L a r c o i d e a, derived from 

 Actolarcus (the lentelliptical Actissa) by the formation of a simple fenestrated shell 

 around the lentelliptical central capsule. But possibly also some species of Cenolarcus 

 may be derived from Coccolarcus or Larnacilla by reduction and loss of the medullary 

 shell (compare Cenolarcus triaxonius, n. sp.). 



' Cenofarc us = Hollow basket ; x-niii, 'accqxos- 



