26 BULLETIN OF THE 



mouth. Mouth anterior. Teeth with broad, backward-extended bases 

 and slender cusps. Spiracles present. One dorsal, without a spine. 

 An anal fin. Caudal without a pit at its root. The first gill-cover free 

 across the isthmus. Intestine with a spiral valve. Anterior basibran- 

 chial cartilages present. 



Chlamydoselachus. 



Six gill openings. Opercular flap, first gill-cover, broad. Teeth sim- 

 ilar in both jaws ; each with three slender, curved, subconical cusps, sep- 

 arated by a pair of rudimentary denticles, on a broad base. No median 

 upper series of teeth in front ; a series on the symphysis below. Mouth 

 wide, without labial folds at the angles. Pupil horizontally elongate. 

 Fins broad ; caudal without a notch. Basihyal elongate. The name is 

 derived from X'^/Jti^'s, a mantle, or frill, and o-eA.a;(os, a shark- 



The position of Chlamydoselachus in the system of recent sharks is 

 not difficult to determine. Six gill-openings and the structure of the 

 brain at once remove it from the others, and place the genus near the 

 outlying genera Ilexanchus and Heptabranchias. As it differs more 

 than they do from other sharks, it lies farther from the main body of 

 the Galei. The shape of the body, position of the mouth, articulations 

 of the jaws, dentition, squamation, lateral line, pelvis, tail, and tropeic 

 folds furnish characters sufficient to establish the distinctness of both 

 genus and family. By such features as the chondrification, the unseg- 

 mented notochord, the elongate bulbus, numerous cardiac valves, open 

 lateral line, and the squamation, its rank is detennined to be somewhat 

 lower than that of the Notidanidse. Possessing, as in the shagreen and 

 certain cephalic peculiarities, more in common with Rhina (Squatina), 

 though not at all closely related, it naturally falls into place in our lists 

 between the latter and the mentioned family. 



What gives the new type a far greater importance than its standing 

 among recent forms, however, is found in its affinities to some of the 

 earliest known sharks, those of the Middle Devonian. Close affinity to 

 the genus Cladodus makes it in present knowledge " the oldest living 

 type of vertebrate." 



In connection with its relationship to the early Selachia a number of 

 perplexing questions present themselves for answer. Further accumula- 

 tions of fossil material will be needed to determine how far success has 

 attended the attempts here made to solve some of the problems. 



