CEPHALOCHORDA. 353 



centre of the Indian Ocean about half-way between Madagascar and Australia. The depth at 

 which it was taken cannot be stated with any certainty, as it came up in a dredge which 

 had been working in 800 fothoms. It may thus have been taken on the bottom or enclosed 

 in the net as it was hauled up. 



The form on examination proves to be a specimen of B. pelagicum, the only other known 

 example of which was taken by the Challenger in 1875 in the open Pacific, and which was 

 described by Gunther in the Challenger Report on the pelagic fishes. The specimen considered 

 here was unfortunately in so bad a condition, both externally and internally, that it was 

 impossible to work out its internal anatomy, either by sections or by mounting whole. The 

 Challenger specimen was almost equally bad, so that until fresh and better preserved specimens 

 are obtained, we must remain ignorant of its organisation, which should prove interesting. 



Fig. 82. Branchiostomum pelagicum. View of the preserved specimen. The branchial region is seen on the 



under side to the left. 



In length the specimen is 21 mm. and it possesses 60 myotomes (the exact number is 

 uncertain owing to decay), while the Challenger specimen had 67 myotomes. The tail fin is 

 broad and lance-shaped, the dorsal and ventral halves being equal (Fig. 82). For the size 

 of the animal it is extraordinarily well-developed, a condition which lends colour to the view 

 that it is a true pelagic organism. A very narrow dorsal fin runs forward from the tail to 

 the head, and an equally narrow ventral fin is present, the precise length of which could 

 not be made out. 



The shape of the head is peculiar, being tapered and ending in a pronounced snout. 

 No trace of buccal cirri could be seen either when viewed sideways or when cut into sections. 

 It would indeed seem that the absence of buccal skeleton is a real character, and not due 

 to maceration or loss, none being found in the Challenger specimen. The structure of the 

 branchial region could not be well seen, owing to the bad preservation of the inner parts 

 of my specimen. It appeared however to be peculiarly small in extent, and quite similar to 

 Gunther's figure of the Challenger specimen. 



