24 PROF. HUXLEY ON THE SPECIFIC AND GENEBIQ 



the median keel of the tail, which commences with the thirty-first 

 row. The number of scutes in each row is as follows : — 



Eows. Scutes. Rows. Scutes. 



1,2,3,4 6 25,26 5 



5,6,7,8,9,10,11 10 27,28 4 



12,13 8 29,30 4 



14, 15 6 



16,17,18 4 31,32,33,34..... 5 



19 6 The rest of the tail is 



20 8 w^anting. 



23,24 6 



Throughout the dor so-lumbar and sacral regions (i.e. up to the 

 nineteenth row), the median scutes are hardly keeled at all, while 

 the outer ones are the more strongly carinate the more external 

 they lie. 



In the caudal region, the second scute from the middle line, in 

 the twenty-third row, has a strong keel and angulation, which 

 grows stronger in the corresponding scutes up to the thirtieth 

 inclusive, until the superior and lateral faces of these scutes, in the 

 twenty-ninth and thirtieth rows, are inclined to one another at a 

 right angle and very strongly keeled. I have said that, as a rule, 

 the median line is occupied by a suture between two median scutes ; 

 but in the caudal region*, in the twenty-fifth row (which corre- 

 sponds with the sixth caudal vertebra) the two median scutes are 

 replaced by one flat scute, so that there is no suture in the middle 

 line. In the twenty-sixth row there is a similar arrangement, but 

 the flat scute is smaller ; and in the twenty-seventh no trace of it 

 is left, so that the strongly keeled lateral scutes meet in the middle 

 line, which is again occupied by a suture. This continues up to 

 the thirty-first row, when the median scute reappears as a thin 



^JTertical plate, broader below and in front, where it articulates tsrith 



ethe median lateral scutes, than above and behind, where it exhibits 

 a free edge only covered by the horny epidermis. It is thus that 

 the serrated dorsal crest of the tail is formed. The scutes of the 



'Urest exhibit only very small round and distant pits. 



?^ The ventral shield begins in the neck just behind the level of 



baii i^-::-.: ..- : -. ...;... ::,^ -; :....; : _ ; .. -i:.. ,,-.- 



• The second and thii'd cervical rows in Caiman palpehrosus and trigonatus 

 also contain a median scute, and consequently an odd number of scutes. In 

 Caiman trigonatus, the third to the ninth supra-caudal rows have each a median 

 single scute. 



