REPORT ON THE TUNICATA. 15 



Pyrosomes, published in 1815. In this work the true nature of Pyrosoma is 

 recognised, some of tlie former errors in the description corrected, find the genus is 

 removed from the Radiata and placed in the Mollusca alongside Salpa. A detailed 

 description, with figures, of the new species Pyrosoma (jiganteum is given, and some 

 of the features in which it differs from the other known species Pyrosoma atlanticvtn 

 and Pyrosoma elegans are pointed out. The figures illustrating this paper are good,' 

 and are of great assistance in determining the species. 



Savigny, to whom we naturally turn for accurate information upon every genus of 

 the Tunicata kno^ai in his day, gives a detailed account of the structure of Pyrosoma 

 gigantenm in his second memoir.''' His investigations are quite independent of those 

 of Lesueur, and were made upon specimens from Nice sent by Risso to Cuvier, and 

 placed by the latter in the hands of Savigny. The genus was then for the first time 

 properly characterised, his description forming, in fact, with a few slight alterations 

 and additions, the definition now employed. 



Savigny divided the species into two groups : — 



I. Pyrosomata verticillata— containing the single species Pyrosoma elegans, 



Lesueur ; and 

 II. Pyrosomata paniculata — containing the two species Pyrosoma atlanticum, 

 Peron, and Pyrosoma giganteum, Lesueur. 



Of these two sections of the genus, the first is characterised by having the 

 Ascidiozooids arranged in verticils or regular rings, some of which at regular intervals 

 project beyond the others. The second section has the colony formed of Ascidiozooids, 

 not verticillate, but arranged in very irregular circles in which the more prominent 

 ones are irregularly scattered. If this character, the arrangement of the Ascidiozooids 

 in the colony, is to be depended upon, then none of the Challenger specimens belong 

 with certainty to the first section of the genus, and a specimen in the Zoological 

 Museum of University College, Liverpool, obtained, named as Pyrosoma elegans, from 

 the Zoological Station, Naples, does not belong to that species, since its Ascidiozooids 

 are irregularly scattered. There are also other points in which it does not agree with 

 the descriptions of Lesueur and Savigny. 



Of the two species belonging to the second section, Savigny distinguishes Pyrosoma 

 oManticum from Pyrosoma gigayiteum^, as having a more conical shape, and as differing 

 in the form of the external projecting ends of the Ascidiozooids — those of Pyrosoma 

 atlanticum being subulate, while in Pyrosoma giganteum they arc hemispherical or 

 conical, the larger ones having their extremities lanceolate and finely denticulate. 

 Savigny divided the specimens of Pyrosoma giganteum which he examined into three 

 kinds or varieties, which will be discussed farther on under the species. 



' For a detailed criticism of Lesueur's paper, see Huxley, Tnmx. Linn. Soc. Lond., vol xxiii. p. 194, 18C2. 

 - Jlemoires, pp. 5^ et scq. 



