36 
THE VOYAGE OF H.M.S. CHALLENGEE. 
this may probably depend upon some error in the determination. In general, 
the descriptions of Lesson are very defective, but even he mentions the small 
tube-like tubercles on the dorsal surface, observed by myself in the Challenger 
specimens. 
As a rule, the species of the genus Ghirodota are very difficult to distinguish 
from each other. The one form passes imperceptibly into the other in such a 
manner that no special specific characteristics can be drawn up. The repre- 
sentatives of this genus are, as it were, in a state of evolution, only few species 
having been hitherto differentiated. However, our present knowledge is too 
unsatisfactory to decide on the validity of several so-called specific characters. 
The number of tentacles and digits as well as the colour, the arrangement of the 
wheel-papillae, &c., seem to be subject to great variation. If this be so, it may 
follow, for instance, that Ghirodota purpurea is the Antarctic form of the Arctic 
Ghirodota pellucida, and that Ghirodota rotifera of Pourtales unites these two 
• extremes. 
III. Tentacles fifteen to twenty. 
Chirodota c^fscoZor, Eschscholtz, 1829; Grube, 1850 and 1851; Ludwig, 1881. 
Liosoma sitchaense, Brandt, 1835 (according to Ludwig). 
Tentacles twelve (seldom eleven or fifteen), each with twelve to fourteen digits. A 
row of white papillae along three of the interambulacra. 
■ Habitat. — Sitka (Brandt and Eschscholtz), Sea of Okotsk (Grube). 
Chirodota incongrua, Semper, 1868. 
Tentacles sixteen, each with eighteen to twenty digits. Wheel-papiUae in five not 
very crowded interambulacral rows. Six larger and two smaller Polian vesicles. 
Habitat. — Camiguin in Philippine Islands (Semper). 
Chirodota variahilis, Semper, 1868 ; Ludwig, 1881. Chirodota refuscens, Brandt, 1835 
(according to Ludwig ^). 
Tentacles seventeen to eighteen, each with twenty-two to twenty-four digits. Wheel- 
papillae equally distributed all over the body. Six to twelve Polian vesicles. 
Besides the wheels, slightly curved ribs or rods are present, with the serrate 
ends slightly enlarged. 
Habitat. — Mariveles, Philippine Islands, and Cape York (Semper), Bonin Island 
(Brandt), Sunda Strait (Sluiter), Hong Kong (Ludwig), Japan, Timor, and Batavia 
(Ludwig). 
The specimen obtained from Australia differs slightly with regard to its tentacles and 
deposits, whence Semper considers it as a variety. 
(Mus. Holm.) One individual with seventeen tentacles, dredged at Singapore. 
' Accordin',' lo Ludwig, A.“pidochir mertensii of Brandt is either ’a Synapta or a Chirodota. It is captured at Sitcha. 
