XIII 



PHYLUM CHORDA TA 



189 



and has the appearance of a second or external lower jaw. In 

 Chimau'a the snout is blunt, in Harriotta long and pointed ; in 

 Callorhynchus it is produced into a rostrum, from the end of which 

 dei^euds a large cutaneous flap (B.ic) abundantly supplied with 

 nerves and evidently serving as an important tactile organ. 



A still n'iore important difference fioiu Elasmobranchs is the 

 possession of only a single external branchial aperture (/'/•. ('2^.), 

 owing to the fact that a fold of skin, the 02Jcrculum {op.), extends 





P<^tJ- 



^sm 



Flu. S47.— A, Chimacra xnonstrosa ; Li, Callorhynchus antarcticus. ". <i. autwior 

 clasper : c. <■/.' poucli for its reception ; hi: aji. branchial aporturu ; ■■. /. caudal tiu ; c. ;'.' its 

 whip like proloiigatiuii ; d. f. 1, d. f. J, doi-.sal tins ; /,-. rl . frunt.il clasper ; I. /., I. /.' labial 

 folds ; I. I. lateral line ; na. dp. nasal aperture ; o/>. operculum ; prt. f. pectoral fin ; jii-i. 

 pterygopodia ; 2n-.f. pelvic fin ; t. teeth ; tc. tactile (lap ; v. f. ventral fin. (A, after Cuvier.) 



backwards from the region of the hyoid arch and covers the true 

 gill-slits, which thus come to open into a common chamber situated 

 beneath the operculum and communicating with the exterior by 

 a single secondary branchial aperture placed just anterior to the 

 shoulder-girdle. Equally characteristic is the circumstance that 

 the urinogenital aperture is distinct from and behind the anus, 

 there being no cloaca. 



There are two large dorsal fins (cl.f.l,d.f.;J) and a small ventral 

 {v. /.) ; the caudal hn (c.f.) is of the ordinary heterocercal type 



