THE VOYAGE OF H.M.S. CHALLENGER. 
836 
arranged in more or less distinct layers ; but the individual chamberlets are irregular 
both as to size and shape, and the layers in which they are combined lack the evenness 
and symmetry which is an invariable feature of the kindred porcellanous forms. 
“ But little was known of the arenaceous Rhizopoda constituting the families 
Astrorhizidse and Lituolidse before the ‘ Porcupine ’ expedition of 1869, and the 
variety of form which they exhibit, their diversity of structure, and the extent of their 
Fig. 305. — Eastigerina peJagica (d’Orli.) (murvayi, Wyv. Thoms.), with floating apparatus and pseudopodia extended, 
as found floating on the surface. , 
geographical distribution, were previously not so much as suspected. The fine series of 
Arenacea obtained by the £ Porcupine ’ has been enriched at every point by the Challenger 
dredgings. To the ‘ Porcupine ’ genera Botellina, Marsipella, Pilulina, and Cyclam- 
mina; the Challenger has added the curiously fashioned Aschemonetta, the flexible weed- 
like Rhizammina, and the adherent branching Sagenella, together with a long array of 
fresh species of previously known genera, 
