1750 THE VOYAGE OF H.M.S. CHALLENGER. 



branches of different lengths ; the anterior (or pectoral branch) twice as long (in the free part) as 

 the diameter of the fork-thicket, the posterior (or tergal branch) three times as long. 



Dimensions. Diameter of the whole body 20, of the fork-thicket 3'2. 



Habitat. Indian Ocean (Sunda Strait), Eabbe, surface. 



Genus 732. Ccelothauma, 1 Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. 



Jena, Dec. 12, p. 6. 



Definition. C celographida with two paired lateral frenula on each galea, with- 

 out external lattice-mantle, armed with twelve styles (three pairs of styles on each 

 valve). 



The genus Ccelothauma differs from the preceding Codotholus, its ancestral form, in 

 the possession of twelve long, prominent styles, six of which are opposite in three pairs 

 on each valve. In the single species observed each of the four main tubes (opposite in 

 pairs on the frontal corners of the two galese) is simply forked, as in Ccelotholus; but 

 whilst in this latter all eight styles remain simple, in Ccelothauma the anterior (or 

 pectoral) branch only is simple, the posterior (or tergal) branch is again forked. 



1. Ccelothauma duodenum, n. sp. (PI. 122, figs. 3-5). 



Twelve styles straight, of different lengths. Two short bilateral main tubes arise opposite in 

 pairs from the two frontal corners of each galea, and are divided into an anterior and posterior 

 branch. The anterior or pectoral branch is simple, and twice as long as the diameter of the 

 fork-thicket. The posterior or tergal branch is again forked near the base, and its two divergent 

 branches are three times as long as the diameter of the fork-thicket. All twelve styles are densely 

 studded with anchor-pencils of nearly equal size. 



Dimensions. Diameter of the whole body 21, of the fork thicket 3'5. 



Habitat. South-Western Pacific (east of New Zealand), Station 169, depth 700 fathoms. 



Genus 733. Caslothamnus, 2 Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. 



Jena, Dec. 12, p. 6. 



Definition. C celographida with two paired lateral frenula on each galea, 

 without external lattice -mantle, armed with sixteen styles (four pairs of styles on 

 each valve). 



The genus Ccclothamnus differs from its ancestral form, Ccelotholus, in the duplication 

 of the number of long verticillate styles, which are prominent over the surface of the 



1 Ccelothauma = Hollow wonder; xo/Ao;, tfai^a. ^ Ccelothamn-us = Hollow thicket; xoiXoj, &.pm',. 



