I. Subfamily Cœlotholida. Rhinocanna of each valve with two paired lateral frenula. The distal ends of the dichotomous brushes are not united by anastomoses, and form an outer bivalved fork-thicket. | ||||||
| Eight paired styles (four on each valve), | ||||||
| 731. Cœlotholus. | ||||||
| Twelve paired styles (six on each valve), | ||||||
| 732. Cœlothauma. | ||||||
| Sixteen paired styles (eight on each valve), | ||||||
| 733. Cœlothamnus. | ||||||
II. Subfamily Cœloplegmida. Rhinocanna of each valve with an odd sagittal frenulum. The distal ends of the dichotomous brushes are united by anastomoses, and form an outer bivalved lattice-mantle. | ||||||
| Mantle with six styles. | ||||||
| One odd and two paired styles on each valve, | ||||||
| 734. Cœlographis. | ||||||
| Mantle with eight styles. | ||||||
| Two odd and two paired styles on each valve, | ||||||
| 735. Cœlospathis. | ||||||
| Mantle with ten styles. | ||||||
| One odd and four paired styles on each valve, | ||||||
| 736. Cœlodecas. | ||||||
| Mantle with twelve styles. | ||||||
| Two odd and four paired styles on each valve, | ||||||
| 737. Cœlostylus. | ||||||
| Mantle with fourteen styles. | ||||||
| One odd and six paired styles on each valve, | ||||||
| 738. Cœloplegma. | ||||||
| Mantle with sixteen styles. | ||||||
| Two odd and six paired styles on each valve, | ||||||
| 739. Cœlagalma. | ||||||
Subfamily 1. Cœlotholida, Haeckel.
Definition.—Cœlographida with two paired lateral frenula on each galea, and with free terminal branches on the hollow radial tubes, without an external lattice-mantle. Eight to sixteen long styles are prominent over the surface of the fork-thicket, which is composed of the caudal brush and the dichotomous basal branches of the styles.
Genus 731. Cœlotholus,[[347]] n. gen.
Definition.—Cœlographida with two paired lateral frenula on each galea, without external lattice-mantle, armed with eight styles (two pairs of styles on each valve).
The genus Cœlotholus and the two following genera form together the subfamily Cœlotholida, the hollow tubes of which do not communicate by anastomosing branches, and therefore form no lattice-mantle, as in the following subfamily Cœloplegmida. Another important difference between these two subfamilies of Cœlographida is found in the arrangement of the main tubes and their connection with the rhinocanna. In all Cœlotholida a pair of divergent frontal styles arise from the truncate oral side of each galea, and are connected with the mouth of the rhinocanna by two lateral convergent paired frenula (right and left); whereas the characteristic odd nasal style, which in all Cœloplegmida arises from the sagittal apex of each galea and is connected with the mouth of the rhinocanna by an odd sagittal frenulum, is always wanting. The total number of long verticillate styles, which project over the outer surface of the fork-thicket, is eight in Cœlotholus, whilst it is twelve in Cœlothauma, and sixteen in Cœlothamnus. The two latter may be derived from Cœlotholus, as the common ancestral genus of this subfamily.
1. Cœlotholus octonus, n. sp. (Pl. [122], figs. 1, 2).
Eight styles of equal length, regularly zig zag, twice as long (in their free part) as the diameter of the loose fork-thicket. Anchor-pencils gradually tapering from the proximal towards the distal end. Each of the four primary frontal tubes (to the right and left of each valve) is simply forked, and the pectoral (anterior) branch of each tube is so diametrically opposed to the tergal (posterior) tube of the other side, that they form together a double cross.
Dimensions.—Diameter of the whole body 12, of the fork-thicket 2.5.
Habitat.—South-Eastern Pacific, Station 300, depth 1375 fathoms.