478 Memoir Sears Foundation for Marine Research 



Disc: length 56.0, 55.0. 



Sfiout length: in front of orbits 0.9, 0.8; in front of mouth 9.3, 9.4. 



Orbits: horizontal diameter 4.6, 4.7; distance between (middle) 10.4, 10.4. 



Spiracles: length 3.0, 3.1; distance between 14.9, 15.0. 



Mouth: breadth 10.5, 10.9. 



Exposed nostrils: distance between inner ends 8.1, 8.4. 



Gill openings: lengths, ist 2.8, 2.7; 3rd 3.0, 3.8; 5th 2.2, 2.0; distance between 



inner ends, ist 15.6, 15.6; 5th 10.9, 10.7. 

 Dorsal fin: vertical height 4.2, 4.5; length of base 6.3, G.d. 

 Pelvics: outer margin 9.1, 9.6. 

 Distance: from tip of snout to center of cloaca 48.4, 50.2 ; from center of cloaca 



to origin of caudal spine 11.4, 10.6. 



Except for the numbers and shapes of the teeth, the specimens listed as R. brasil- 

 iensis resemble R. bonasus so exactly in general appearance and in proportionate dimen- 

 sions that to describe them in detail would merely repeat the description of R. bonasus. 

 The teeth, as stated previously (pp. 467, 477), are normally in nine series in each jaw. 

 But abnormalities are so frequent that only four out of six free-living specimens seen 

 by us have the normal number; one has eight series in the lower jaw, nine in the upper; 

 one has ten in the upper jaw, nine in the lower; and one jaw (not stated whether upper 

 or lower), apparently referable to R. brasiliensis, has been reported as having the normal 

 four series on one side of the median series but eight on the other side, making a total of 

 13 series.^* In specimens with the normal number of nine series, the teeth of the median 

 series at birth are about 3.5-4.0 times as broad (transversely) as long (anteroposteriorly) ; 

 those of the first series outward are about 2—7 times as broad as long; those of the next 

 series on either side are about 1.5 times as broad as long. But in larger specimens the 

 teeth of the median series are 5-7 times as broad as long; those of the first series out- 

 ward are about 3.5-5.0 times as broad as long, and those of the next series on either 

 side are about 1.7-2.0 times as broad as long. Normally the teeth in the outermost two 

 series are about as broad as long from birth onward. In individuals with more series of 

 teeth than normal, those in the series next to the median are likely to be wider than 

 normal ; but those of the second series outward from the median series are narrower than 

 normal in specimens with fewer than nine series, the outermost series being very small. 

 These variations meet the spacial requirements of an increase or decrease in the number 

 of series with the relative breadth of the mouth remaining the same. The final number 

 of series of teeth, as well as the pavement-like arrangement of those of the more poste- 

 rior rows, is established in embryos not more than about 200 mm wide. But the teeth of 

 the two or three anterior embryonic rows are minute, rounded, loosely spaced, and 

 lost before birth. Such is the case in R. bonasus also. 



54. According to Woodward (Ann. Mag. nat. Hist., [6] j, 1888: 282), who pictured this specimen and discussed its 

 dentition at some length, it was "evidently referable to the Brazilian species R.jussieui." But its geographic origin 

 was not definitely stated. See also Gudger (J. Elisha Mitchell Sci. Soc, 4g, 1933: 82, fig. 16). 



