JURA. LUMINOUS ANIMALS. 189 



of the rigid portion which attends that one. From the 

 latter it is as readily distinguished by its longitudinal con- 

 catenation ; since, in that species, the individuals adhere 

 by their sides, so as to form a row in a lateral direction ; 

 while there are at the same time important differences 

 in the structure of the two. 



I had occasion to remark of this animal, that, like the 

 Medusae and analogous tribes, it cannot bear to be con- 

 fined in a limited portion of water; as it died, even in 

 the ship's bucket, in less than half an hour ; a very 

 remarkable circumstance in the economy of these imper- 

 fect animals. 



Hitherto, this genus is only known as the inhabitant 

 of hot climates and of the Mediterranean sea. I found 

 it in great abundance in the harbours of Canna and 

 Campbelltown ; rising to the surface in calm weather, and 

 crowding the water, as the Medusae often do at the same 

 time of the year. It may be called Salpa ? moniliformis, 

 and denned as follows : 



S. Ovato-lanceolata, ano fusco, absque appendice ter- 

 minali.* 



I was desirous of observing whether this animal, like 

 many other of the marine worms, emitted light, but had no 

 opportunity of ascertaining the fact ; as they seemed 

 always to retire to the bottom at sunset, and those which 

 were taken on board died, as I have already observed, in 

 a very short time. 



The phenomenon of luminous water is exhibited 

 throughout these seas during the autumnal season with 

 great brilliancy ; increasing with the appearance of the 

 Medusee, and diminishing when they disappear. 



This fact has been known to naturalists, at least since the 



* The difficulty of distinguishing the several genera of mollusca which 

 resemble this, and the obscurity in which the subject is still involved, 

 render it necessary to speak with hesitation concerning the genus of this 

 animal. The present description, although imperfect, will nevertheless 

 suffice to point it out to the attention of naturalists. 



