28 Bulletin 4/, United States National Museum. 



Cabcharhinina:: 

 cc. Spiracles obsolete; lower teeth narrower tlian upper teeth. • 



g. Angle of mouth without groove or with nierelv a slight depression, whicb docs 

 uot extend along either jaw. 

 ?». First dorsal fin inserted posteriorly, nearer ventrals than pectorals; embryo 

 not joined to the uterus by a placenta; slender sharks, with very strongly 

 serrated teeth. Prion ack, 24. 



hh. First dorsal inserted anteriorly, nearer pectorals than ventrals; embryo (sd 

 far as known) attached to the uterus by a placenta. 

 t. Teeth all serrate more or less, often entire; in the very young. 



CAUCHARIIINrS, 2.'). 



a. Teeth of upper jaw serrate at base only; lower teeth entire, erect. 



Hy'poprion, 20. 



Hi. Teeth all entire at all ages, and nearly all erect. APRioNonoN 27. 



gg. Anglo of mouth provided with a more or less distinct groove which extends along 



one or both of the jaws; teeth entire, or very nearly so, more or less obliquely 



placed, their points turned away from the median line; embryo (so far as 



known) with a placenta. Scoliodon, 28. 



i8. MUSTELUS, Cuvier. 



(Dog Sharks.) 



Mustehia, CuviF.R, Kegno Animal, Kd. 1,128, 1817, [rnusleliis and canis). 



Mimtctiis, Gill, Proc. Ac. Nat. Sci. Phila., 1804, 148, (restricted to (•(wis and its relatives, the 

 allies of Mustelus being called Pletiracromylon). 



Body elongate, slender ; snout compara.tively long and flattened ; mouth 

 crescent-shaped, -with well-developed labial folds; teeth small, many- 

 rowed, flat and smooth, rhombic, arranged like pavement, alike in both 

 jaws, and blunter than in any other sharks; eyes large, oblong; spiracles 

 small, just behind the eyes; pectoral fins large; first dorsal large, uot 

 much behind pectorals ; second dorsal somewhat smaller ; anal opposite 

 second dorsal and still smaller; ventrals well developed; basal lobe of 

 caudal almost obsolete, the tail nearly straight ; embryo not attached to 

 the uterus by a placenta. Small sharks, among the smallest of the Ameri- 

 can species, {mustelus, a weasel or marten ; the same word used for shark, 

 as is the synonymous word (/aleus.) 



a. Middle of first dorsal evidently nearer posterior root of pectoral than anterior root of ven- 

 tral; snout long, its length from mouth more than width of mouth; teeth blunt. Em- 

 bryo uot examined, probably as in M. catiu. ltjnulatus, 30. 



nil. Middle of first dorsal about midway between pectorals and ventrals (as above measured). 

 First dorsal higher than long, the tip of anterior lobe reaching, when depressed, beyond 

 tip of posterior lobe, its free margin deeply incised, its base 2% times in interval between 

 dorsals; teeth blunt. canis, 31. 



30. MUSTELCS Ll-'XCLATUS, Jordan & Gilbert. 

 (Gato.) 



Free margin of fins concave; first dorsal high, its narrow anterior lobe 

 reaching tip of the slender posterior lobe when deflected, the fin about as 

 high as long; interval between dorsals 2| times base of first; lower lobe 

 of caudal pointed ; tail 5 in body, its terminal lobe more than ^ its length ; 

 pectoral rather sharp, its free margin incised, its tip about reaching mid- 

 dle of dorsal. Embryo unknown (probably without placenta). Very 



