16 Bulletin 47, United States National Museum. 



. Order D. DIPLOSPONDYLI. 

 (THE NOTIDANOID SHARKS.) 



Sharks with the palatoquadrate apparatus articulated or connected with 

 the postorbital processes of the skull; branchial apertures in increased 

 number, 6 or 7: only 1 dorsal fin. Vertebral column imperfectly seg- 

 mented so that from each segment 2 neural arches and 2 vertebral bodies 

 arise. Among existing sharks this group contains 2 families. Numerous 

 genera represented by fossils seem allied to these, which are among the 

 " oldest living vertebrates." (rftTrA&of , double ; airbvdvTioc, vertebra; Noti- 

 danus, (vuridavbc, dry back) is a Greek name of some shark, in Atheneus.; 



a. Body greatly elongate, almost eel-shaped ; dorsal, anal, and ventrals close together on pos- 

 terior part of body ; teeth in -the 2 jaws alike ; mouth anterior. 



CHLAMYDOSELACUID.S:, v. 

 aa. Body moderately elongate ; teeth in the 2 jaws unlike ; mouth inferior. 



HEXANCHID.E, vi. 



Family V. CHLAMYDOSELACHID^E. 

 (THE FRILLED SHARKS.) 



Body elongate, slender, suggesting the form of an eel. Head broad, 

 depressed. Eyes lateral, without nictitating membrane. Nasal cavity 

 separate from that of the mouth. Mouth anterior. Teeth with broad, 

 backward-extended bases and slender cusps. Spiracles present. Gill 

 openings 6. One dorsal fin, without spine ; anal fin present. No pit at root 

 of caudal. First gill membrane free across the isthmus. Intestine with a 

 spiral valve. Anterior basibranchial cartilages present. 



This family contains a single species, recently discovered by Mr. Garman, 

 from whose papers this account is taken. It inhabits the open sea, and 

 may not occur in American waters. 

 Chlamydoselachidse, GARMAN, Bull. Essex Inst., 1884, 47, and elsewhere. 



10. CHLAMYDOSELACHUS, Garman. 



Chlamydoselachus, GARMAN, Bull. Essex Inst., Jan. 17, 1884, 47, (anguinens). 



Opercular flap forming a broad frill over first gill opening. Teeth simi- 

 lar in both jaws, each with 3 slender, curved, subconical cusps, sepa- 

 rated 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. One species 

 known, inhabiting waters of some depth in the open sea. An extinct 

 species, Chlamydoselachus lawleyi, Davis, has been described from pliocene 

 deposits in Tuscany. (xha/Ltv?, mantle or frill; ae^a^of, shark.) 



16. CHLAMYDOSELACHUS ANGUINEUS, Garman. 



Dorsal fin small, opposite the anal, which is more than twice its size; 

 pectorals small, placed low ; ventrals large, placed far back, opposite 

 anal. Eye small. Gill openings large, curved, oblique, all of them before 



