REPORT ON THE TUNICATA. 221 



tentacles are numerous, and a little irregular, lmt not of two sizes arranged symmetrically. 

 The dorsal lamina has its ribs very closely placed (PI. XXXIV. fig. 6), and the edge is 

 distinctly serrated. 



Two specimens of this curious species were found at Port Jackson, Australia, at a 

 depth of 6 fathoms. 



Pachychhvna, n. gen. 



Sub-genus Pachychlmna, Herdman, Prelim. Rep., Proc. Roy. Soc. Edin., 1879-80, p. 461. 

 Body attached, sessile. Branchial aperture eight-lobed, atrial six-lobed. 

 Test cartilaginous, very thick, solid and opaque. 

 Branchial Sac longitudinally plicated. Internal longitudinal bars bearing large 



papillae at the angles of the meshes. Stigmata straight. 

 Dorsal Lamina in the form of a membrane. 

 Tentacles simple. 

 Viscera large, placed on the left side of the branchial sac. 



In the first part of the Preliminary Report, I distinguished the three species forming 

 the present genus from the other species of Ascidia, on account of the remarkable thickness 

 and solidity of the test. This feature suggested Pachychlmna as an appropriate sub-generic 

 title. As, however, I have not recognised any other sub-genera among Simple Ascidians, 

 and as it is objectionable to introduce new grades into classification, unless absolutely 

 necessary, it will be more convenient to consider Pachychlmna of generic rank, at least 

 until some form is found which links it to Ascidia. That such a form may be found I 

 have no doubt. Pachychlcena and Ascidia are closely allied, and although the specimens 

 of the two genera in the Challenger collection are clearly distinguishable, it is easy to 

 imagine a species, or a series of species, uniting their characters, and forming a gradual 

 transition from the one to the other. 



The three species of Pachychlcena described below agree in the following particulars : — 

 The body is sessile and attached, but of different shapes. The test is thick and opaque, 

 and of a firm cartilaginous texture. The branchial sac is longitudinally plicated, and 

 is of considerable thickness. The meshes are transversely elongated (PI. XXVIII. 

 figs. 2 and 7, and PL XXIX. fig. 4), and have large papillae at their angles; no smaller 

 intermediate papillae are present. The specimens of two of the species were all more or 

 less injured, so that the exact determination of the body form is impossible, but the single 

 specimen of the remaining species, Pachychlama oblonga, is in perfect condition. 



Pachychlcena oblonga, Herdman (PI. XXIX. figs. 1-9). 



Pachychlama oblonga, Herdman, Prelim. Pep., Proc. Roy. Soc. Edin., 1879-80, p. 461. 

 External Appearance. — The body is irregularly oblong in shape, widest about the 

 middle, and narrowing somewhat towards the anterior end, which is obtuse and flattened ; 



