REPORT ON THE PELAGIC FISHES. 43 



Beside these species there is represented a third by a specimen labelled " Deep haul, 

 1000 fathoms. Pacific, July 26, 1875." On this date the Challenger was in lat. 23° 3' 

 N., long. 156° 6' W., a few degrees north of Honolulu. This specimen, therefore, was 

 captured in the open sea, at a great distance from land ; but it would seem to be 

 uncertain whether it came from that great depth or from the surface. On the one hand, 

 as living specimens of Branchiostoma are always observed to sink to the bottom after 

 some almost convulsive motions to wriggle themselves towards the surface, it is difficult 

 to see how a Lancelet could maintain itself at the surface in the open ocean ; on the other 

 hand, the perfect condition of the delicate fin-fringe would suggest that the specimen 

 could not have been hauled up from so great a depth, without showing signs of injury. 

 However this may be, the specimen, although approaching in form, and in the 

 number of myocommas, Branchiostoma helcheri, differs from it in the shape of the 

 caudal fin, and especially from this and all the other species by the absence of buccal 

 cirrhi. 



Branchiostoma pelagicum, n. sp. (PL VI. fig. B). 



The specimen is 10 mm. long and 1 mm. deep ; it was mounted in glycerine for the 

 microscope at the time of its capture. 



The anterior end of the notochord is enveloped in a very strong sheath ; the posterior 

 (|- mm.) is not covered by the myocommas, which leave ofi" abruptly, and extends right to 

 the hind margin of the caudal fin. Eye distinct ; nerve-cord with minute pigment-spots 

 arranged intracentrally with regard to the myocommas. Dorsal fin-rays low, but very 

 distinct, about five to each myocomma. The dorsal fin-fringe commences to become 

 distinct about the twenty-seventh myocomma, gradually becoming somewhat higher 

 behind. Its rise is more abrupt where it passes into the caudal fin, which is paddle- 

 shaped and bilaterally symmetrical with regard to the notochord. The lower half of the 

 caudal passes uninterruptedly into the ventral, in which no rays are developed. This 

 fin seems to be continued forward as a very low fringe for some distance beyond the 

 supposed position of the atrial pore. Nearly the whole of this fringe shows a minute 

 vertical striation, especially in its higher portions. 



The number of myocommas is sixty-seven, of which fifteen belong to the taU. How 

 many should be attributed to the portion between vent and atrial pore is uncertain on 

 aocount of the difficulty in ascertaining the position of the latter. I have been unable to 

 make out this pore, and infer its position to be opposite to the thirty-sixth myocomma 

 only from analogy or comparison with other species, and from a slight contraction of 

 the muscular layer at this spot. 



Buccal tentacles are absent; this cannot be due to the age of the individual, as they 



