Genus 270. Spongolarcus,[[309]] n. gen.
Definition.—Larcarida with lentelliptical spongy shell, containing a central cavity of the same form, without medullary shell (without radial spines).
The genus Spongolarcus differs from Cenolarcus (its probable ancestral form) only in the development of spongy framework forming the wall of the hollow lentelliptical shell. It corresponds, therefore, to Plegmosphæra among the Sphæroidea, and to Spongellipsis among the Prunoidea. From these two similar spongy Sphærellaria it differs in its characteristic lentelliptical form, with three dimensive axes of unequal length.
1. Spongolarcus lentellipsis, n. sp.
Spongy network of the shell very loose, its meshes fifteen to twenty times as broad as the bars. Surface of the shell nearly smooth; diameter of its internal cavity twice as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 3 : 4.
Dimensions.—Length 0.16, breadth 0.12, height 0.08; thickness of the spongy wall 0.05.
Habitat.—Pacific, central area, Station 274, surface.
2. Spongolarcus triaxonius, n. sp.
Spongy network of the shell rather loose, its meshes twelve to sixteen times as broad as the bars. Surface of the shell rough; diameter of its internal cavity about eight times as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 2.5 : 3.
Dimensions.—Length 0.25, breadth 0.2, height 0.16; thickness of the spongy wall 0.025.