1734 THE VOYAGE OF H.M.S. CHALLENGER. 



The genus Ccelodoras is the simplest form of the Ccelodendrida, and may be regarded 

 as the common ancestral form of this and of the following family. It differs from all other 

 members of these two families in the simple shape of the hollow radial tubes which arise 

 from the galea, and are neither branched nor forked ; the galea is very small, a flat 

 triangular cap. Ccelodoras may be derived immediately from Concharium or Con- 

 chonia (p. 1723), by development of the galea and the radial tubes. 



1. Ccelodoras hexagraphis, n. sp. 



Three straight, cylindrical, equidistant hollow tubes arise divergent from the three corners of 

 each galea, and are about as long as the diameter of the valves, at the distal end armed with a 

 spinulate knob. The odd sagittal (or caudal tube) is directed backwards, the two paired (or pectoral) 

 tubes, forwards. 



Dimensions. Diameter of the valves 0'16, length of the tubes 0'2. 



Habitat. Central Pacific, Station 266, depth 2750 fathoms. 



2. Ccelodoras octographis, n. sp. 



Four hollow cylindrical tubes, slightly curved, arise divergent from each galea, and are about 

 one and a half times as long as the diameter of the valves, at the distal end knob-shaped, and 

 armed with four crossed, recurved teeth. Two anterior (or pectoral) tubes arise from the two 

 frontal corners of the galea basis, and diverge forwards to right and left. Two posterior tubes (a 

 sagittal and a caudal) arise from the posterior corner of each galea, and diverge in the sagittal plane 

 backwards. 



Dimensions. Diameter of the valves 0'2, length of the tubes 0'3. 



Habitat. Central Pacific, Station 272, depth 2600 fathoms. 



Genus 728. Ccelodendrum, 1 Haeckel, 1860, Monatsber. d. k. preuss. Akad. 



d. Wiss. Berlin, p. 801. 



Definition. Coe lo dendr ida without external lattice-mantle, with branched 

 radial tubes, the hollow branches of which are free and never connected by anastomoses. 



The genus Ccelodendrum is the first described form not only of the family 

 Coelodendrida, but of all P h ae o c o n c h i a or bivalved PH^ODAEIA ; it is also the most 

 common form of this group, and represented by ten different species, some of which are 

 cosmopolitan, very common, and widely distributed. In my first description of 

 Ccelodendrum I confounded it erroneously with some forms of Ccelodasea and Ccelo- 

 graphis, the separated fragments of which I had found entangled between the branches 

 of the former. The first figures of Ccelodendrum are given in my Monograph, in 1862, 



1 Ccelodendrum = Hollow tree ; xoiAoj, Stio*. 



