IBT. 11 NORTH AMERICAN TADPOLES — WRIGHT 33 



row, which goes from above the middle of the insertion of the tail 

 musculature to back of the eye, where a supraorbital and an infra- 

 orbital branch goes forward. 



Mouth parts. — Teeth -| or |-. Upper labium edged by a fringe of 

 teeth, the fringe longer than the beak. Below either end of this 

 fringe is a long row of teeth about two-fifths to one-third the length of 

 the upper fringe. The median space one-half to one time the length of 

 the lateral row. Usually it is less than once the lateral row, while in R. 

 pipiens it is almost invariably more than once the lateral row. In 

 many tadpoles as they approach transformation there appear in 

 either corner a short third row of labial teeth on both sides or some- 

 times on one side only. Also in mature tadpoles it not infrequently 

 appears. For example, in 1912 we secured 23 tadpoles of this species, 

 of which 6 had the third row on either side, this row 0.33-0.24 the 

 length of the second row, and in 3 specimens the third row was 

 present on only one side. On the lower labium are three rows of 

 teeth. The third row is shorter than the single row of labial papillae, 

 one-third to two-sevenths shorter than the second or first rows, or 

 about one-sixth to one-fifth shorter than the horny beak. First and 

 second lower labial rows about equal and slightly longer than beak. 

 First one is sometimes subdivided in the middle. 



Measurements. — Length of body (19.0-25.0 mm.) in tail (28.5-37.5 

 mm.) 1.35-1.66, average 1.53. Width (1.0-16.0 mm.) of body in its 

 own length 1.56-2.1, average 1.77. Depth (9.0-15.0 mm.) of body 

 0.8-1.36 in body width, average 1.1. Depth of body 1.5-2.3 in body 

 length, average 1.95. Depth (10.5-16.5 mm.) of tail in length of 

 tail 2.0-2.88, average 2.65. Muscular part (6.0-9.5 mm.) 1.35-2.35 

 in depth of tail, average 1.80. Spiracle 1.2-1.7 nearer base of hind 

 legs or vent region (8.0-14.0 mm.) than the tip of the snout (12.5-16.0 

 mm.), average 1.46. Spiracle 1.1-1.86 nearer eye (5.0-9.0 mm.) than 

 base of hind legs or vent, average 1.46. Eye 1.15-1.3 hearer to tip of 

 snout (5.0-7.0 mm.) than to spiracle (5.0-9.0 mm.), average 1.2. 

 Nostril to snout equal to nostril to eye each 3.0-5.0 mm. Mouth 

 (3.0-5.0 mm.) usually 0.9-1.6 larger than internasal space (2.2-5.0 

 mm.), average 1.25. Mouth contained 1.4-2.0 (average 1.68) in 

 interorbital distance (5.5-7.5 mm.). Internasal space contained in 

 interorbital space 1.4-2.3, average'l.95. 

 The dimensions of the largest tadpole are: 



Mm. 



Totallength 62. 5 



Body length 25. 



Body depth 15. 



Body width IG. 



Tail length 37. 5 



Tail depth 13. 



Musculature of tail 9. 5 



Spiracle of snout 15. 



Mm. 



Spiracle to vent 14. 



Spiracle to eye 7. 5 



Eye to snout 6. 5 



Eye to nostril 4. 5 



Nostril to snout 3. 5 



Mouth 4. 5 



Interorbital distance 7. 



Internasal distance 5. 



6359—29 3 



