566 PROCEEDINGS OF THE NATIONAL MUSEUM vol. its 



length of distal margin: Measured as the length of a straight 

 line from the most distal point on the anterior margin to the tip of 

 the inner corner. 



Pectoral width: Measured as the length of a line perpendicular 

 to the anterior margin and extending to the tip of the inner corner. 



Clasper length: Measured as the distance between the two points 

 of a pair of dividers with one point in the axil of the pelvic fin and the 

 other on the tip of the clasper. 



During the course of this study I noticed the lack of male specimens 

 with developing claspers. All males I examined had either juvenile 

 or completely formed claspers. Plotting clasper lengths (as percent 

 t.l.) against total length (see species accounts) established this im- 

 pression. An explanation of the phenomenon probably lies in the 

 fact that claspers do not mature gradually with the growth of the 

 individual. Their growth to maturity begins abruptly and is com- 

 pleted in a very brief period of time and generally simultaneously 

 within a given population (year class) of males. Some males with 

 intermediately developed claspers undoubtedly will be collected, but 

 only few in comparison with those having juvenile or completely 

 developed claspers. Thus, puberty in males is of a much shorter 

 duration than periods of complete immaturity or maturity. Pleath 

 (1960) noted that the claspers of Squalus acanthias and Mustelus 

 canis mature rapidly with little increase in body length at time of 

 maturation. 



Caudal fin — 



length of the upper lobe: Measured as the length of a straight 

 Une from the upper caudal origin to the distal tip of the upper lobe, 

 length of the lower lobe: Measured as the length of a straight 

 line from the lower caudal origin to the distal tip of the lower lobe. 



dorsal tip to notch: Measured as a straight line from the tip 

 of the upper lobe to the distal tip of the notch. 



notch depth: Measured from the distal tip of the notch to the 

 proximal end of its incision. 



Dorsal-pectoral ratio. — This ratio is found by dividing the total 

 length of the first dorsal fin by the length of the anterior margin of 

 the pectoral fin and multiplying by one hundred (table 3). 



Counts. — Teeth: In this study only the upper jaw is considered 

 to have a symphysial tooth, and there is always one, never more. 

 The teeth on the outer margin of each jaw form a "row" and a single 

 tooth of the row with those teeth aligned inward to it comprise a 

 "series." 



It was found that total counts of teeth in a row of either jaw gave 

 more constant results than counts from a single ramus of either jaw. 



The most posterior teeth of a ramus frequently are very small 



