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.
2. Cœlotholus cruciatus, n. sp.
Eight styles of equal length, straight, twice as long (in their free part) as the diameter of the dense fork-thicket. Anchor-pencils of about equal size throughout their whole length. Each of four primary frontal tubes is divided into two equal, widely divergent branches; the anterior branches of the right side are diametrically opposed to the posterior branches of the left side, so that all eight together form a double cross.
Dimensions.—Diameter of the whole body 20, of the fork-thicket 4.0.
Habitat.—South-Western Pacific (off Sydney), Station 164A, depth 1200 fathoms.
3. Cœlotholus ancoratus, n. sp.
Eight styles of different lengths, slightly curved. Anchor-pencils gradually tapering from the proximal to the distal end. Each of the four primary frontal tubes is divided into two divergent
