STYLASTKRIDAE 



prominences, are mainly found on the front and lateral sides of the branches and are here irregularly 

 arranged between the gasteropores. The gasteropores are sometimes provided with one or a few 

 tabulae; both the gasteropores and dactylopores are sometimes in open communication with the ir- 

 regular, large, central canals in the colony, exceptionally also with each other directly. The gastero- 

 zooids have no tentacles. The dactylozooids, which are attached by a narrow base in the pore, have 

 a central lumen. — The ampullae are deeply placed. The male gonophores are composite and are 

 developed singly in the ampullae. — The surface of the colony is smooth, not reticulate. 



Colour (in alcohol): yellowish dirty gray. 



Occurrence: at Florida and in the Northern Atlantic in depths of 190 — 700 m. 



Material: 



"Ingolf" St. 55 6 3 °3 3 ' N, i 5 °o 2 ' W. depth 594 m. 5.9°. C. 



- 57 6 3 ° 35 ' - 13W - 658 - 3.4 . C. 



On the Ingolf Expedition some fragments and a complete colony of this peculiar species, which 

 at first sight is all too readily regarded as a Bryozoon, were taken. The intact colony (PI. I, figs. 1 and 2) 

 shows the marked tendency of the species to branch dichotomously. This characteristic is also clearly 

 seen in Pourtales' and Duncan's drawings. How far this is more than a specific character we are 

 unable at present to determine with certainty, as only a few quite small fragments have been found 

 of the other species of the genus Pliobothrus. Pourtales' drawing of Pliobof/irus tubulatus (1871, 

 PI. 4, fig. 9) suggests however, that we have here a specific character, the fragment figured at any rate 

 is not branched dichotomously. 



There is in general no very marked main stem in Pliobothrus symmetricus, nor do its branches 

 show any regular difference in thickness. In this regard the intact colony of the "Ingolf differs from 

 those described earlier; the unbranched, basal part of the colony may best be described as a kind of 

 main stem, although its dimensions do not in reality differ obviously from those of the branches. 

 The other, somewhat smaller fragments are not so distinctly and simply fan-shaped. Single branches 

 show a tendency to new fan formations in planes almost at right angles to the primary plane of the 

 colony. As no other difference could be detected between the colonies, however, this must be 

 considered as purely chance variations in the colonial form. — There is a sharply marked difference 

 between the front and back of the colony. On the front the pores are evenly and densely distributed 

 over the whole of the surface and here the dactylopores are present in large numbers; on the back, 

 on the other hand, the dactylopores have practically disappeared and the number of gasteropores is 

 also somewhat reduced. The difference becomes the more pronounced, the nearer we come to the base 

 of the colony, the pores on the hind surface becoming more and more reduced both in number and 

 size. In the above-mentioned, more irregularly branched fragments, all difference between the front 

 and back disappears on the branches which emerge from the primary plane of the colony; the pores 

 are evenly and densely distributed on the whole surface of these branches. 



Under a low magnification already (PI. I, fig. 3) we notice larger and smaller pores, which, 

 however, are not arranged in rows or systems. The larger pores — gasteropores — have their opening 

 plane at the level of the colony surface, whilst the small pores — dactylopores -- are found on the 

 top of small, conical protuberances. As mentioned above, the number of the dactylopores especially 



