8 Memoir Sears Foundation for Marine Research 



tain a single series of fin rays only; rostral fin, with anterior part of dorsal fin, lacks fin 

 rays; dorsal fin-ray chambers much more numerous than myotomes, with four or five 

 chambers to each myotome; the atrial chamber extends posterior to atriopore as a single 

 blind sac as far as the anus; olfactory pit present. 



Genera. Two genera, Branchiostoma and Dolichorhynchus, are commonly recognized 

 in the family and are separated as indicated in the following icey. In addition, a new sub- 

 genus of Branchiostoma has recently been proposed under the name Amfhifleurichthys^'' 

 for a species in which "the form is more elongated and less robust" than in Branchiostoma, 

 "with the myotomes more acutely tapering at each end of the animal," and in which the 

 "caudal fin is reduced to a low fold."" But the differences appear to us specific, rather 

 than generic. 



Key to Genera 



I a. Rostral process, including anterior end of notochord, extends far beyond preoral 

 hood. Dolichorhynchus Willty, 1901 



Ceylon. 



lb. Rostral process, including anterior end of notochord, extends only a short distance 

 beyond preoral hood. Branchiostoma Costa, 1 834, p. 8. 



Genus Branchiostoma Costa, 1834 



Branchiostoma Costa, Ceni. Zool., 1 834: 49; type species, B. lubricum Costa. Naples. 



Generic Synonyms: 



Limax Pallas, Specil. Zool., Fasc. 10, 1774: 19, pi. 1, fig. 11; for L. lanceolatus Pallas, Cornwall; not Limax 

 Linnaeus, 1758. 



Giuterobranchus ? Rasch, Mag. Naturvid., Physiogr. Foren. Christiania, 12 (2) 2, 1836: 325, footnote; evi- 

 dently Branchiostoma, from the excellent account, but only provisionally identified by that author; west- 

 ern Norway; not Gasterobranchus Bloch, 1795, which is a synonym for the cyclostome Myxine Linnaeus, 

 1758. 



Amfhioxus Yarrell, Brit. Fish., 2, 1836: 468; type, Limax Icmceolatus Pallas, 1774. 



Amfhifleurichthys (subgenus) Whitley, Aust. Zool., 7 (3), 1932: 256; type, A. minucauda Whitley. Queens- 

 land. 



Generic Characters. The rostral process, including the anterior end of the notochord, 

 projects for only a short distance beyond the preoral hood; the characters are otherwise 

 those of the family. 



Range. European coasts from northern Norway to the Mediterranean, the Black Sea 

 and tropical West Africa; western Atlantic from Chesapeake Bay'* to the Rio de La Plata 

 (including Bermuda); Pacific coast of the Americas from Middle California to Chile; 

 Japan; China; East Indies; Philippines; Queensland; India; Ceylon; Madagascar; East 

 and South Africa. 



17. Whitley, Aust. Zool., 7 (3), 1932: 256. 



1 8. Lancelets were said by Garman (in Kingsley, Stand. Nat. Hist., 5, 1885 : 62) to range as far north as New York; 

 but we find no positive record of any member of the group in the western Atlantic farther north than Chesa- 

 peake Bay. 



