•_'-_S THE VOYAGE OF H.M.S. CHALLENGER. 



bythiidse. It certainly has no near affinities with either the Molgulidse or the Cynthiidse, 

 and I have placed it here amongst the Ascidiidse because we have no evidence that it 

 possesses the power of reproducing by gemmation. Setting this negative character aside, 

 the genus seems to me to be more closely allied to the Clavelinidse than to the Ascidiidse, 

 and if allowed to remain in the latter family, must be regarded as an abnormal member, 

 not conforming to some of the most important characteristics, and displaying features 

 which show it to be an annectent form between the Ascidiidse and the Clavelinidae. It 

 agrees with the latter family in having the apertures circular and not lobed, and differs 

 from all the other Ascidiidse in having no internal longitudinal bars in the branchial sac. 

 Further remarks upon the peculiarities and affinities of the genus will be found below the 

 descriptions of the two species. 



ILjpobijthius calycodes, Moseley (PI. XXXVII. figs. 1-5). 



Ili/pobi/thim calycodes, Moseley, Trans. Linn. Soc. Lond., ser. ii., Zool., vol. i. p. 287. 



This is one of the two species described by Professor Moseley in his paper " On two 

 new Forms of Deep-Sea Ascidians, obtained during the Voyage of H.M.S. Challenger," 

 published in December 1876. As I have been able, from an examination of the single 

 fragmentary specimen, to add little to Mr. Moseley's excellent account of this species, I 

 shall merely transcribe the most important parts of that description, and refer for further 

 ]iai'tieulars to the original paper. 



" The animal has the form of an inverted cone, compressed laterally so as to have an 

 oval transverse section. From the apex of the inverted cone is continued a cylindrical 

 stem, which is enlarged towards its inferior extremity (PI. XXXVII. fig. 1). The 

 test is hyaline and extremely transparent. Where it is simple it is thin and flexible, but 

 in certain spots it is strengthened and rendered stiff by the presence in it of rounded or 

 plano-convex masses or plates of denser tissue, which are tough and cartUaginous in con- 

 sistence, and which are disposed over the surface of the test in a nearly symmetrical 

 manner. These plates are extremely conspicuous when the test is held up to the light 

 and viewed by transmitted light, because they refract the light strongly ; and the pattern 

 formed by them on the test when thus viewed has a very peculiar appearance. The dis- 

 position of the plates on the ventral surface of the body wfil be seen from figure 1 , that 

 on the dorsal surface from figure 2 (PI. XXXVII. ). 



" A series of globular lobes range on either lateral margin of the body, and give it 

 here considerable rigidity, and a ridge of highly condensed tissue runs across the body at 

 the upper margin of its dorsal surface. A series of flattened plates is disposed over the 

 inferior region of the ventral aspect of the body, whfle the superior region of the same 

 aspect, covering the gill sac and perforated by the inhalent aperture, is entirely devoid 

 of plates, very thin and flexible, and most perfectly transparent. On the dorsal aspect of 

 the body a very large plate occupies the middle line inferiorly, whilst immediately above 



