292 Papers from the Marine Biological Laboratory at Tortugas. 



grinding surface extends back over 10, although the next 5 posterior teeth 

 are scarred. The outer right and left thirds of teeth one and two have been 

 broken off. This plate is fully three-eighths of an inch thick, the enamel 

 constituting two-eighths and the dentine one-eighth, but it is very interesting 

 to note that in the outermost and deepest worn tooth the enamel is but 

 one-eighth and the bony portion two-eighths of an inch thick. The upper 

 jaw, which seems to have suffered but little abbreviation, is 3)^ inches 

 long, while its width is 2^ inches. It has 16 teeth, 6 of which are in the 

 grinding surface proper, though the next two teeth show rough usage. 



It is of course understood that the teeth of this ray, like those of all 

 Elasmobranchs, grow from membrane in the rear and that as they wear 

 out or are broken off in front the growth of those behind keeps the number 

 fairly constant. It must also be made clear that the teeth numbered in the 

 jaws described are the total number found by clearing away the overlying 

 fleshy "gum" or membrane. The apparent number gotten by counting 

 those visible in the mouth of the fish would be less by some 4 or 5 teeth 

 probably. This fact may be alleged in part proof of Ruppell's (1835) 

 "short" count of the teeth of his ray. He counts 7, but shows 8 teeth in 

 the upper jaw, while in the lower jaw the numbers are 7 and 6 respectively. 



The dried jaws of my Key West specimens will now be described. Three 

 of these were rather small, but the fourth was full-grown. All were males. 



Ray No. i was 33 inches wide and 243^^ long. Its upper jaw is i J^ inches 

 long and 1 3^^ wide. It has 17 teeth, of which the forward 6 are deeply 

 worn practically all the enamel of the outermost tooth having disappeared. 

 The lower jaw measures 3J4 by i inches and has 20 teeth; 10 of these 

 show wear, Nos. 6, 7, 8, and 9 are so worn as to be depressed below the 

 general level. Attached to the corners of the outermost tooth are fragments 

 of another, the central and pointed half of which is gone. 



Specimen No. 11 was 32 inches wide by 23 long. Its upper jaw is i^ 

 inches long by 1% wide. It has 14 teeth, of which the outer 5 show hard 

 usage, a fragment being broken off the right-hand end of the foremost tooth. 

 The lower jaw is 3]^ inches long by i wide. It has 20 teeth, of which the 

 12 outer show wear, this being greatest in the region of Nos. 4 to 8 inclusive, 

 counting from before backwards. The left third of the first tooth is gone. 



My third specimen for 191 3 was 34 inches wide and 24 long. Its teeth 

 are the green ones previously referred to. Its upper jaw, composed of 16 

 teeth, is 2 inches long by 1 3^ wide. Its 6 foremost teeth are badly worn, 

 the wear stopping abruptly on the seventh. The outer ends of the front 

 tooth are gone. The lower jaw plate, made up of 21 teeth, is 3^ inches 

 long and i]/^ wide. The grinding surface includes the first 10 teeth, and 

 in teeth 6, 7, 8, and 9 there is a marked depression. The outer tooth has the 

 central half only present, the ends having broken away. 



Key West ray No. iv was the largest Aetobatus I have ever had and its 

 jaws are in proportion. It was 62 inches wide and 32 long, and weighed 

 120 pounds. Its upper jaw-plate measures 33^ by 2^ inches. Of its 16 



