26 



FISH GALLERY. 



Chlaiuy- 



dosela- 



chus. 



Noti- 

 danus. 



Notidani (Notidanid Sharks). 



The Notidani constitute a small suborder 

 of archaic Sharks in which the gill-openings 

 are six or seven on each side of the body. 

 The vertebral column is imperfectly segmented, 

 and the centra are feebly if at all calcined ; 

 there is but a single dorsal fin, which is set 

 rather far back, opposite the anal fin. There 

 is no nictitating membrane or third eyelid, 

 such as occurs in some Sharks (<?. g. 67, 

 Wall-case 2). There are two families, the 

 Chlamydoselachidse and the Notidanidse. 



The family Chlamydoselachidse includes but 

 a single genus, Chlamydoselachus, a long, 

 slender-bodied Shark (specimen 12, and 

 fig. 12) found in the deep seas of many 

 parts of the world, and first obtained off the 

 coast of Japan in 1884*. The head is depressed, 

 and the mouth is terminal. There are six pairs 

 of gill-openings, with backwardly directed frills 

 or flaps of skin, whence the popular name 

 "Frilled Shark " given to this fish. The 

 skull is hyostylic, i. e. the jaws are suspended 

 from the cranium by means of the upper 

 element of the hyoid arch (for illustration of 

 "hyostylic" see specimen 18). The teeth 

 are of primitive character and several rows 

 are simultaneously in use ; the crown consists 

 of three slender curved cusps, separated by a 

 pair of small denticles ; the embedded bases 

 are broad and backwardly extended, and 

 overlap one another in the gum. 



In the Notidanidse the skull differs from that 

 of the previous family in being " amphistylic," 

 i. e. the jaws are connected with the cranium 

 or brain-case in two ways, by a direct articu- 

 lation between the upper jaw and the optic 

 region of the cranium, and by means of the 

 hyomandibular cartilage, or upper piece of the 



fc/ 



11/ 



CO 

 h3 



I 



71 



t-t- 

 P4 



