EEPOET ON THE HOLOTHUEIOIDEA. 
51 
Genus 4. Trochostoma, Danielssen and Keren, 1877, 1882. 
Eetractors absent or rudimentary. Calcareous ring with five bipartite, posterior pro- 
longations. Tentacles fifteen, brancbed, digitate. Anus often with teetli-like 
papillm. Body-wall mostly rough. Deposits — ellipses of a reddish colour and 
concentric structure alone : or tables alone ; or both kinds together. 
A. Deposits — Ellipses and Tables. 
Trochostoma horecde {21oIj)ad{a), Sars, 1859, 18G1 : Danielssen and Koren, 1882. Mol- 
jyadia oolitica, Selenka, 1867 {partim). Haplodactyla oolitica, Semper, 1868 
{partim). 
Tentacles with tliree (?) digits. Deposits — small red, crowded ellipses ; tables com- 
posed of an irregular network of a triangular or rounded form representing the 
disk with large holes and carrying a spire terminating in two slightly spinous 
tops ; tables having the disk elongate fusiform with some central holes, and a 
spire terminating in a single shghtly spinous top, these being present in greater 
number at the ends of the animal. 
Halitat . — Finmark (Sars), Barents Sea (Hoffman), Kara Sea (Stuxberg), Florida Eeef 
(Pourtales). 
(Mus. Hohn.) Numerous specimens from the Arctic coast of Siberia. As it seems 
to me, each short tentacle has a very short, broad, middle digit, and a narrower 
on each side, thus three digits. Anus with five (?) short papillje. The red 
bodies in the perisome seem mostly to be collected in groups. 
Trochostoma thomsoni, Danielssen and Keren, 1878, 1882. 
Several localities south and north of the Arctic circle in the North Atlantic Ocean, at 
depths from 136 to 658 fathoms (Danielssen and Koren). 
So far as I can discover, this form must be very nearly allied to the former, and it 
seems to me almpst impossible to point out any difi'erence of such importance as 
to justify their separation into two distinct species. I do not think the very 
inconsiderable differences in the conformation of the deposits, &c., sufficient to 
establish a new species. 
Trochostoma violaceum [Alolpadia), Studer, 1877. Trochostoma horecde, Danielssen and 
Koren, 1879, 1882 {partim). 
Tentacles with three short digits. Deposits — round or elongate reddish bodies of a 
concentric structure ; very large, smooth fusiform rods or three-armed bodies 
without spire, but with a few holes at their middle ; and small, very few scattered 
