296 CEYLON PEARL OYSTER REPORT. 



depressiusada, Heller, and Styela areolata, Heller, both collected by Professor 

 Schmakda, and Ecteinascidia thurstoni, which I described, in 1890, from a colony- 

 obtained by Mr. Edgar Thurston on the pearl banks in the Gulf of Manaar. 

 Another species of Ecteinascidia described below, although from the same locality, 

 seems to be quite a distinct form. 



Since 1891, Sluiter has described 28 new species of Ascidians from the shores of 

 South Africa (mostly Capetown, Durban and Mozambique), but these, although in the 

 Indian Ocean, are still between two and three thousand miles distant from Ceylon. 

 Sluiter has also described a large number of new species from Malaysian seas, as the 

 result of the " Siboga " expedition. A few of these occur in the present collection, 

 but the majority of the Ascidians of the Malay Archipelago seem to be distinct from 

 those of the coast of Ceylon, although closely allied forms. It is interesting to have 

 re-found the two species originally brought from Ceylon by Schmarpa, and also 

 to have obtained the recently described, curious, compound Ascidian Hypurgon, 

 I. B. Sollas, which forms a skeleton with its own hardened faecal pellets. 



Sluiter and I seem to have expressed somewhat divergent views, in our recent 

 works, on the geographical distribution of Tunicata, but the differences may possibly 

 be more apparent than real. They are due to the vibrations of the scales, as first one 

 and then the other of us brought to be weighed fresh batches of new species from 

 different parts of the world. Successive advances in knowledge led to changes in 

 opinion. As the result of my examination of the " Challenger" material, I came to 

 the conclusion, quite justified by the facts then known, that the fixed Tunicata were 

 more abundant and larger in southern than in northern or tropical seas. A few 

 years later Sluiter, as the result of his explorations round the island of Billiton 

 (Dutch East Indies) described a large number of tropical new species of Ascidians, 

 and so was led to correct my opinion which he did vigorously. After another 

 interval of years, the large collections belonging to the Sydney Museum passed 

 through my hands, and this enabled me to describe such a considerable number of 

 additional southern species as to cause me, after careful weighing of the evidence, 

 including, of course, Sluiter's tropical forms, to come to the conclusion that the 

 balance was again in favour of the far south. Since then several notable additions 

 have been made to our knowledge of the Indo-Malayan fauna ; and the rapidity with 

 which the number of known species is being added to by each successive expedition 

 indicates that our knowledge of the. distribution of the group is still far from complete. 

 But whatever result the actual number of species from the tropics and from the polar 

 regions may give us in the future, I believe that the Ascidian fauna of the far south 

 is characterised by the abundance of individuals and by their large size. 



Believing that in the present state of our knowledge of the species of Tunicata 

 careful drawings are quite as important as descriptions, and realising from my own 

 experience how valuable some detail of an illustration may be in the identification of 

 a species, I have endeavoured, in the present case, to illustrate fully the appearance 





