306 LEPTOCARDII. 



Sub-Class IV LEPTOCARDII. 



Skeleton semi-cartilaginous and notochordal : destitute of jaws or ribs. 

 Brain absent. Blood colourless, and distributed by pulsating sinuses. Respira- 

 tory and abdominal cavities confluent ; numerous branchial clefts,'and the water 

 discharged by an opening in front of the vent. 



Family I CIRROSTOMI. 



An elongated compressed body ; having a low rayless dorsal fin, continued 

 round the tail past the vent to the respiratory opening. Mouth a longitudinal 

 slit on the inferior surface with cirri. Eyes rudimentary. Vent near the end of 

 the tail. 



Genus I Branchiostoma, Costa. 



Amphioxus, Yarrell. 

 Definition as in family. 



1. Branchiostoma lanceolatum, Plate CLXXIX, fig. 4. 



Limax lanceolatus, Pallas, Spicil. Zool. x, p. 19, t. i, f. 11. 



Branchiostoma lubricum, Costa, Cenni, Zool. Nap. p. 49. 



Amphioxus lanceolatus, Yarrell, Brit. Fish. (ed. 1) ii, p. 468 (ed. 2) ii, p. 618 

 (ed. 3) i, p. 1 ; Thompson, Nat. Hist. Ireland, iv, p. 268 ; Couch, Fish. Brit. Isles, 

 iv, p. 415, pi. ccxlviii. 



Brachiostoma lanceolatum, Gray, Catal. Chond. p. 150; White, Catal. p. 146; 

 Giinther, Catal. viii, p. 513. 



This creature is introduced here, due to its being included in other works on 

 British fishes. The structural resemblance between Amphioxus and the Ascidians 

 was pointed out by Goodsir. In 1866-67, Kowalevsky published in the " Memoirs 

 of the Academy of St. Petersburg," essays on the development of this animal, and 

 of Ascidians, as spanning the gulf between the vertebrates and invertebrates, and 

 giving positive foundation to the doctrine of a phylogenetic connection between 

 apparently entirely different circles of life. 



Of a compressed form, pointed at both ends ; vent at the commencement of the 

 last quarter of the body. The abdominal pore for the exit of the water from the 

 branchiae, opens at about the middle of its entire length. Colours opalescent. 



Habits. Couch found his specimen in December, 1831, at Polperro, bui'ied 

 in a small quantity of sand, at about 50 feet from the receding tide, and on turning 

 over a small flat stone that was on the sand, its tail was seen. The specimen 

 fio-ared among some others, was dredged at Mevagissey in 1883, and when 

 brought on shore with the remainder of the refuse, showed great signs of activity, 

 and rapidly disappeared in the moist sand. Mr. Ogilby observed that in an aqua- 

 rium they buried themselves in the gravel, emerging as soon as darkness came on, 

 but the approach of a candle caused them at once to again retreat into the gravel. 



Habitat. Cosmopolitan in most temperate and many tropical regions. It has 

 been recorded from Norway and Sweden, and along our shores in the Isle of Man 

 (Forbes) : Firth of Clyde (White) : the Moray Frith : St. Andrew's (Mcintosh) : 

 Redcar in Yorkshire, Hampshire, along the west of Cornwall and Guernsey. 

 Also along the south coast of Ireland ; and Mr. Douglas Ogilby on March 16th, 

 1868, obtained two between the tide-marks in Portrush harbour : they were about 

 2^ inches in length. 



