27 6 THE VOYAGE OF H.M.S. CHALLENGER. 



longitudinal bars are more than usually close. In Molgula piriformis there are only three 

 internal longitudinal bars in each of these regions, but, as I have shown elsewhere, 1 in 

 the case of Styela grossularia, a more rudimentary condition even may be traced through 

 a series of gentle gradations into a well-developed fold. 



The dorsal tubercle is very variable in the Molgulidae. In typical species of the genus 

 Molgula it is usually cordate or reniform in outline, with both horns coded inwards, but 

 not forming large spirals. In Molgula forbesi (PL V. fig. 11), we find a comparatively 

 simple tubercle, with one horn turned out and one in, while in Molgula gigantea, and in 

 Ascopera gigantea (PL III. fig. 5), the spirals are very large, quite as large as in any of 

 the Cynthiidae, which are usually supposed to have the most complicated tubercles. In 

 Molgula pyriformis (PL VI. fig. 3), and Eugyra kerguelenensis (PL VI. fig. 9), on the 

 other hand, the dorsal tubercle is found in the simplest possible condition, namely, as 

 the slightly enlarged aperture of the duct from the neural gland bounded by a plain 

 prominent margin, circular in the one case, and quadrangular in the other. It is rather 

 puzzling to find this simple condition of the dorsal tubercle in the most highly 

 differentiated family of Simple Ascidians, and it does not in the least help us towards a 

 solution of the question why in so many other forms the aperture of the duct of a gland 

 should have acquired such a complicated structure. However, the complexity of the 

 dorsal tubercle is evidently not correlated with that of the other organs, as we sometimes 

 find it in very different conditions in two species which, from the rest of their structure, 

 seem closely allied. 



Among the Cynthiidae the sub-family Bolteninae contains the greatest novelties. It 

 has always been an interesting group, as it contains the rarest and least known forms. 

 The Challenger expedition has revealed the existence of a small group of pedunculated 

 Ascidians, apparently confined to great depths, and having several striking peculiarities. 

 These are more nearly allied to Boltenia than to any other previously known genus, and 

 have been placed in two closely related new genera — Culeolus and Fungulus. 



On account of the great interest attaching to these forms, I have gone into very con- 

 siderable detail in their description, and especially in that of Culeolus murrayi, the only 

 large species of which there were two specimens in the collection. 



As I have shown in the tables given in the two preceding sections of the Report, both 

 the horizontal and the vertical distributions are wide in this genus. The localities of the 

 species are widely separated, and occupy all the great oceans: — one species being from 

 the North Atlantic, off the east coast of North America ; two from the Southern Ocean, 

 between the Cape of Good Hope and Kerguelen Island ; one from the South Pacific, to 

 the north of the Kermadec Islands ; one from the North Pacific, east of Japan 2 ; and one 



1 On Individual Variation in Simple Ascidians, Trans. Lit. and Phil. Soc, Liverpool, 1882. 



2 While these sheets were passing through the press, I received from the Challenger Office a tube containing a 

 small specimen of a Culeolus from this locality (Station 241, 2300 fathoms). It is evidently a new species, and will be 

 described and figured in the second part of this Report. 



