2 THE VOYAGE OF H.M.S. CHALLENGER. 



detail ; and as the descriptions and plates of this part of the collection are now finished, and 

 it may be some months before those of the Ascidise Compositse and the Pelagic Tunicates 

 are completed, it is thought best to publish the Report upon the Ascidias Simplices 

 separately. The Bibliography, however, and some other parts of the Introduction, refer 

 to the whole group of the Tunicata. 



The collection generally was in an excellent state of preservation ; but some few 

 specimens, with exceptionally solid tests, had suffered apparently from the apertures 

 having contracted so completely as almost to exclude the alcohol. The precaution of 

 making an incision in the test had been taken in the case of most of the large specimens. 

 Specimens of a few of the Compound Ascidians and Pelagic forms had also been preserved 

 in absolute alcohol. 



The collection of Ascidiae Simplices consists of eighty-two species arranged in twenty 

 genera. Seventy-four of the species and nine of the genera were new to science. 1 These 

 species added by the Challenger Expedition have not necessitated the formation of 

 a single new family. Although a number of new genera have been required, usually 

 for the forms from great depths, yet these have all found a place in one or other of the 

 four families already known. The new genera have in several cases been of great interest, 

 as they have demonstrated affinities between known forms, and have exhibited combina- 

 tions of characters necessitating in some cases a revision of the definitions of old genera, 

 and even affecting in one or two instances our ideas with regard to the characters of the 

 families. 



In 1876 Professor Moseley described, in the Transactions of the Linnean Society, two 

 very remarkable Ascidians which he had investigated during the voyage of the Challenger. 

 The first of these, Hypobytliius calycodes, belongs to the family Ascidiidas ; the second, 

 Octacnemus bythius, seems to me to be nearer to the Thaliacea than to the Ascidiacea, and 

 consecpiently comes into the second part of this Report. 



The new species are all illustrated and described in detail. Species previously known 

 are not figured, except in cases where they have been imperfectly described, or where the 

 Challenger specimens show some special feature. 



1 Most of these new species were named and briefly described in my four Preliminary Reports upon the collection 

 read before the Royal Society of Edinburgh (see Proc. Roy. Soc. Ediii., Sessions 1880-82). 



