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 Larnacilla-she\\ (compare Cenolarcus triaxonius, p. 607). 



Synopsis of the Genera of the Larcarida. 



I. Subfamily 1 Without radial spines, 266. Cenolareus. 



Cenolarcida. 



Shell simple, latticed (lentelliptical cortical f w ^ radial . m . Larcarium. 



shell). ) 



II. Subfamily 1 



Coccolarcida. Without radial spines, . . . 268. Coccolarcus. 



Shell composed of two or more concentric \ 



latticed shells (inner medullary and outer With radial spines, . . . 269. Larcidium. 



cortical). 



III. Subfamily ~| with aQ internal cayit 2 70. Spongolarcus. 



Spongolarcida. 



Shell spongy, partly or whole composed of a f without m ^^ cayi > 2n ^ larcus _ 



spongy framework. 



Subfamily 1. CENOLARCIDA, Haeckel. 



Definition. L arcarida with simple, lentelliptical latticed shell (cortical shell 

 without a medullary shell). 



Genus 266. Cenolarcus, 1 n. gen. 



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

 medullary shell, without radial spines. 



The genus Cenolarcus begins the group of Larcoideaas the most simple form 

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

 discus among the Discoidea, to Cenellipsis among the Prunoidea. The simple 

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

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

 Probably Cenolarcus is the original ancestral form of the Larcoidea, derived from 

 Actolarcus (the leutelliptical 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.). 



1 Cenolarcus= Hollow basket ; x.-6i, 



