564 PROCEEDINGS OF THE NATIONAL MUSEUM vol. us 



mouth: One point of the dividers was placed on the tip of the 

 snout and the other on the tip of the lower jaw. The distances be- 

 tween the two points was measured. 



gill-opening: (This and the next seven measurements were 

 made with the specimen lying on its side on the measuring board.) 

 A line was drawn across the underside of the head connecting the 

 first gill-opening of each side at the point of its junction with the 

 body. A right-angled triangle was placed vertically on the measuring 

 board with the vertical edge crossing the midpoint of the line. The 

 distance measured was the point where the base of the triangle inter- 

 sected the scale on the measuring board. 



pectoral origin : I found the origin of each pectoral fin by pressing 

 my thumbnail at the junction of the anterior margin of that fin with 

 the body and by locating the point of insertion of the hard internal 

 element comprising that margin. This point on each fin was con- 

 nected with a line across the ventral surface of the specimen, and 

 the midpoint of this line was crossed by the edge of the triangle as 

 above. The distance measured was the point where the base of the 

 triangle intersected the scale on the measuring board. Frequently, 

 because of deformities or poor preservation, one point of origin was 

 much in advance of the other. By measuring the distance to the 

 midpoint of the connecting fine, I obtained the approximate distance 

 to the true origin. 



pelvic origin: This was determined and measured in a wa}'' 

 similar to that of the pectoral origin. 



first dorsal origin: The origin was found in the same manner 

 as that used for the pectorals and pelvics. A line perpendicular to 

 the measuring board (parallel to the anterior end of the board) was 

 extended ventrally over the side of the shark and the vertical edge of 

 the triangle was placed on this line ; the distance along the measuring 

 board was recorded. 



second dorsal origin: The second dorsal origin is a difficult 

 point to establish and can vary considerably with each investigator. 

 I used the point which I subjectively considered to be the point where 

 the sharp anterior edge of the fin first faded out as it passed into the 

 dorsal body contour. A fine was drawn ventrally from this point and 

 the distance to it measured in the same manner as it was done for 

 the first dorsal fin. 



anal origin: This was determined and measured in the same 

 manner as for the second dorsal origin except that it was necessary 

 only to mark the origin and to place the vertical edge of the triangle 

 on it. 



upper caudal origin: This origin was determined to be at the 

 point where the comparatively thin anterior dorsal edge of the upper 



