148 Transactions. — Zoology. 



was impossible to account for some forms which have been 

 found intermediate between the Velasia stage and the adult. 

 Gunther himself, in speaking of one such form, suggests that 

 Velasia may possibly develope a gular pouch later in life, in 

 which case the distinction between the two forms would be 

 doubtful. Ogilby, however, as already noted, actually reverts 

 to the idea of a generic difference between the two. The dis- 

 tinctions upon which the old classifications were based are 

 merely external ones — the shape and size of the oral disc, 

 the position of the teeth, the presence or absence of a gular 

 pouch, and the shape and position of the fins. 



In the Velasia stage the head is small, the oral disc is 

 round and small, and the teeth are closely packed together in 

 rows, whilst in the adult Geotria the head region is enor- 

 mously developed, the oral disc being very large and flattened 

 on the lower margin, owing to the growth of the gular pouch 

 below it ; and the teeth, which, as we have ascertained by 

 careful examination, correspond in number and position to 

 the teeth of the Velasia form, are some distance apart, owing 

 to the growth of the disc between them. The gular pouch is, 

 of course, only fully developed in the adult Geotria, but in- 

 termediate forms have been found possessing a slight gular 

 pouch. 



There is no very great difference between the fins of the 

 Velasia and the adult. They are larger and situated re- 

 latively farther forward in the Velasia, but they change 

 gradually with the growth of the animal, and we have a 

 series of four specimens which exhibit the different conditions 

 of the fins at different stages in life. 



Fourteen specimens of the Velasia which were dissected 

 were found to be sexually immature, males and females, 

 whilst the only two pouched forms which we have dissected 

 are sexually mature, or nearly so. None of the former ob- 

 servers appear to have examined the internal anatomy at all, 

 but have drawn their conclusions from the external differ- 

 ences, probably because of the scarcity of material at their 

 disposal. 



In other respects the Velasia closely resembles the adult, 

 but is longer and thinner. We could not compare the living 

 forms, as we have not yet been able to obtain a fully grown 

 Geotria alive, and we find by experiment that spirit-preserved 

 specimens undergo considerable shortening. 



As the two generic names Velasia and Geotria have been 

 applied to the same animal, we have had to decide which to 

 retain, and, following Giinther's nomenclature, we propose to 

 call the adult form Geotria australis, and to use the term 

 ''Velasia" to distinguish the intermediate form, just as the 

 term " Ammoccetes " is still used to distinguish the larva. 



