TWO Is^EW ATLANTIC DOG SHARKS — SPRINGER 



465 



ridges becoming obscure and even absent on the belly. M. mustelus 

 and M. californicus are not similar with respect to tooth form, but 

 tooth form is an unstable character in the genus. In all the species 

 that I have been able to examine in large series, some individuals, 

 especially young ones, have been found with abnormal teeth of a more 

 definitely tricuspid outhne than would be usual to the species. Young 

 specimens of M. canis frequently resemble young specimens of M. 

 mustelus in this respect, but on the basis of the denticle characters they 

 are easily separable. 



Ml'STELLS SCHMITTI, new species 



Holotype. — An adult male, 742 mm in total length, U.S.N. M. no. 

 106640, collected on the coast of Uruguay by Dr. W. L. Schmitt in 

 1925. 



Paratypes. — Two adult males, each 600 mm in total length, 

 U.S.N.M. no. 87680, collected on 

 the coast of Uruguay by Dr. W. 

 L. Schmitt; an immature male, 450 

 mm in total length, U.S.N.M. no. 

 55582, collected by J. W. Titcomb, 

 at Buenos Aires, Argentina ; a young 

 male, 260 mm in total length, U.S. 

 N.M. no. 87782, taken on the coast 

 of Brazil by Dr. W. L. Schmitt. 



Description. — Similar in form to 

 Mustelus canis but males reaching 

 maturity at a small size (600 mm 

 or less). Snout narrower. Fins 

 broad; lower lobe of caudal not 

 strongly developed, not acute; ori- 

 gin of the first dorsal in advance of 

 the inner angle of the pectoral. Eyes 

 smaller than in M. canis (horizon- 

 tal diameter of orbit 2.5 percent of 

 total length in average of five spec- 

 imens as compared with 3.1 per- 

 cent average for M. canis of com- 

 parable size); horizontal diameter 



of orbit greater than distance between the nostrils. Mouth broadly 

 arched and rounded anteriorly in the adults; outer labial fold longer. 

 Teeth paved, crowns not elevated in adults; accessory cusps present 

 on the teeth of the young specimen, not on the adults examined. 

 Dermal denticles similar in structure on the fiat surfaces of the body, 

 typical 4-ridged, mth ridges reaching about two-thirds of the distance 



FiGURji 55.— Upper: Outline of the tail of an adult 

 male Mustelus griseus Pietschmann, showing 

 rounded lower caudal lobe. Lower: Outline of 

 the tail of an adult male Mustelus norrisi, new 

 species, showing pointed lower caudal lobe. 



