104 PROCEEDINGS OF UNITED .STATES NATIONAL MUSEUM. 



Ill this specimeu the teeth of the upper jaw are broadly triauguhir, the 

 hreadth of the base being about equal to the vertical height, the iuuer 

 margin nearly .straight or slightly convex, the outer margin a little con- 

 cave, but not distinctly notched. Edges of upper teeth conspicuously 

 serrate, especially towards the base. Median tooth very broad and short, 

 serrate, with concave margins. 



Teeth of lower jaw narrowly triangular, with broad bases, which spread 

 out abruptly. Edges of lower teeth weakly serrate ; mediau teeth small, 

 triangular, entire; middle teeth of sides of each jaw largest. Number 

 of teeth about f^. 



The following notes on this specimen were taken by Mr. Gilbert. The 

 measurements were taken with">ut instruments as the shark was lying 

 on the beach, and are not all entirely accurate: 



Head very heavy and short, the snout exceedingly broad and short; 

 its preoral portion much longer, shorter than distance between nostrils, 

 and nearly equal to the length between the inner margins of the pectorals. 

 Eyes on the depressed margin of the head, the nostrils very close to the 

 margin. A short deep fold at angle of mouth, extending a very short 

 distance on each lip. 



Gill openings wide, the last two above base of pectorals, the longest 

 slit about equal to half base of pectoral. 



Origin of tirst dorsal behind vertical from posterior base of pectoral, 

 a distance about equal to a gill-slit, the fin considerably nearer pectorals 

 than ventrals. Anterior margin of dorsal two-thirds anterior margin 

 of pectorals. Anal inserted slightly behind front of second dorsal and 

 somewhat smaJ 

 branchial area. 



Pectorals long, not half longer than broad, their anterior margins 

 convex; inner margin of pectoral about half longer than a gill-slit; 

 about one-third the length of the free edge, which is six-sevenths the an- 

 terior edge. 



Ventrals short; length of anterior margin less than one-third the 

 length of pectorals, nearer second dorsal than first. Distance from an- 

 terior base of ventrals to vertical from tirst dorsal equal to distance of 

 the posterior base from anal. A pit above and belowroot of tail. Cau- 

 dal with lower lobe half length of upper, the lower lobe broadly scythe- 

 shaped. 



This species is rather common about Mazatlan, where it is known as 

 Tibtiron. Its liver is valued for the oil it jiroduces. It was not seen 

 elsewhere. 



The fresh-water shark of Lake Nicaragua {Eulamia nicaraguensis Gill) 

 is closely allied to this species, but apparently distinct. 



Carcharias cethalorus, sp. nov. (2S202, 29549). 



Allied to Carcharias lamia (Risso), but with smaller dorsal and pec- 

 toral fins and longer and more pointed snout. 



