594 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



Order I. NOTIDANI. 



Sharks with the ])ranchial apertures in increased number, 6 or 7; 

 only one dorsal tin. Vertebral cohunn imperfectly segmented so that 

 from each segment 2 neural arches and 2 vertebral l)odies arise. 

 Among existing sharks this group contains 2 families. Numerous 

 genera represented hy fossils seem allied to these and to the Cestra- 

 cioiit types. 



{XoflddUK^'i^ vGotidavog^ dry back, the Greek name of some shark, 

 in Athenseus.) 



(I. I'alatoquadrate apparatus articulated with the postorbital processes of the s^kuU; 

 hody moderately elongate; teeth in the two jawn unlike; mouth inferior. 



Hexanchid.e, I. 



(to. Palatoquadrate apparatus not connected with the skull; body greatly elongate, 



almost eel-shaped ; dorsal, anal, and ventrals close together on posterior part of 



body; teeth in the two jaws alike; mouth anterior.. Chlamydoselachid.e, II. 



Family 1. HEXANCHID.E. 



Body moderately elongate, somewhat depressed anteriorly, tapering 

 toward the caudal tin. Head depressed, o})long, with the snout pro- 

 jecting. Eyes submedian or anterior, without nictitating membrane. 

 Mouth subinferior, large, arched in front; no labial fold. Teeth in 

 the two jaws unlike; in the upper jaw 1 or 2 pairs of awl-shaped teeth, 

 the next six teeth broader and each provided with several cusps, one 

 of which is nnich the strongest. Lower jaw with 6 large comb-like 

 teeth on each side, l)esides the smaller posterior teeth. Spiracles 

 small, on the sid(^ of the neck. Ox\\y one dorsal tin, without spine, 

 opposite the anal, and similar to it. No pit at the root of the caudal. 

 Gill-opcMiings wide, G or 7 in numlier. Viviparous sharks, sometimes 

 reaching a ver}^ large size. Species of the warm seas. 



a. (iill-openings, 7 ( m each side IleptrancJiias, 1. 



1. HEPTRANCHIAS Rafinesque. 



Ilrptravrhi'in Rafinesque, Caratteri, 1810, j). 14 {chiereu^). 

 Nutorlnivchus Aykes, I'roc. Cal. Acad. Sci., I, 1856, j). 72 (inarnldtus). 

 Ifcplamlivs of Authors. 



Gill-openings 7 on each side. Lower teeth uniform in size or 

 decreasing toward corners of mouth; cusps on the cutting edge more 

 or less i-egularly graduat(d. 



{sTCTa^ seven; fiftdyxKv^ giUi^-) 



n. NoTOKiiYNCHUs. Mcdiaii tuotli of lower jaw with the central cusp small or wanting. 

 l>. Color, gray; cusps of most teeth growing smaller from the second deani, 1.. 



