8 PROFESSOR STRUTHERS. 



16 inches out, the depth is 5 inches ; from the most projecting 

 part of the posterior border, more than half-way out, it is 



9 inches; and from between the recurved tips the depth is 



17 inches. The cleft proper is indicated in the first of these 

 measurements, but some may have taken it at the third. 



From tip to tip, straight, the tail-fin is 10 feet 6 inches; 

 between the extreme edges in front of the recurved tips, 11 feet 

 4 inches. 1 The anterior border, after the neck, is convex through- 

 out and very much bent back and also inwards, towards the tip. 

 The falling in is 5 inches, so that the broadest part of the fin is 

 in front of the tip. This great bending back extends on about 



18 inches of the anterior border and 9 inches of the posterior 

 border. The latter undulates; the broadest and most pro- 

 jecting convexity is external to the middle of each half; the 

 concavity between that and the convex boundary of the median 

 cleft is shallow; the concavity next the recurved tip is a 

 deep bay, about 9 inches deep externally and 2 feet in width. 

 The inward direction towards the blunt tip is mainly on the 

 anterior border, but even the posterior border is here directed 

 a little inwards. After the smooth convexity bounding the 

 median cleft, the whole posterior border, out to the tip, is 

 serrated ; about twenty serrations may be counted (on each half 

 of the fin), some large, some small, some sharp, some rounded. 

 The antero-posterior breadths are, in inches, near the median 

 ridge, 36 ; at junction of inner and second fourths, the same ; 

 midway out, 32 J ; at junction of outer two-fourths, 24 ; at nine 

 inches from the tip 7 inches transversely. 



8. SURFACE OF THE ABDOMEN. The umbilical fissure, or 

 groove, 14 inches in length, begins immediately behind the 

 plaitings of the skin. For 8 inches it is a well-marked elliptical 

 fossa, deepest at the anterior end and feels hard at the middle. 



The preputial opening is 3 feet behind the fore-end of the 

 umbilical fissure. The epidermis is whitish here and for 4 or 5 

 inches back. From the preputial opening to the anus there is 

 a groove in which the skin is soft. At the prepuce, at the 

 white part, the groove is at first 4 inches broad and deep, over 



1 Straight from extreme to extreme is the usual way of measuring the tail-fin, 

 but a truer method would be to measure straight from the extreme to the middle 

 of the median ridge, giving the width of each half. Here that is 6 feet 3 inches, 

 giving 12 1 feet as the axis of the entire tail-fin. 



