VOL. LXVIII.] PHILOSOPHICAL TRANSACTIONS. 423 



computer from the perusal of the modes of computation that have been des- 

 cribed in this paper. As to the surveyor, he will strike out other convenient 

 ways of measurement adapted to the circumstances with which the nature of the 

 sun'ey may happen to be attended. 



XXXIF. An Account of the Blue Shark. By W. Watson, Jun. M. D., 



F. R. S. p. 789. 



The fish was taken on the coast of Devonshire. It had got into shallow 

 water, by which accident Mr. Martin, a great lover of natural history, and who 

 happened to be on the shore, was enabled to drag it out by the tail, and to kill it 

 on the spot. Linna3us places this animal in the class of amphibia, under the 

 name of squalus glaucus, and makes use of Artedi's description, viz. squalus 

 fossula triangulari in extremo dorso, foraminibus nullis ad oculos. As this fish 

 is well described by Rondeletius and others, I shall only subjoin the following 

 remarks. There are 2 triangular dents at the origin of the tail, both above and 

 below ; that which is on the back is the larger and deeper. No orifices are to 

 be seen behind the eyes, as is usual with fishes of this genus. Two white mem- 

 branes, one to each eye, perform the office of eye-lids. They are placed be- 

 neath under the external integuments, and move upwards when they cover the 

 eyes. It is furnished with 5 rows of teeth ; these are triangular, and finely 

 serrated. The body is of a fine blue colour, dark on the back, lighter on the 

 sides; the belly and all the under part of the fish white; the fins and tail of a 

 dirty blue ; the colour of the blue part is exactly represented by different shades 

 of indigo blue. When the head was placed downwards, a pretty large white 

 pouch came out of its mouth. iElian supposes this to have served as an asylum 

 to its young brood in time of danger. The length of the fish from the tip of 

 the nose to the end of the tail was 6 feet 8 inches ; the length of the pectoral 

 fin 1 foot 4 inches. It was a female, and weighed 55 pounds. As I have never 

 been able to see an accurate drawing of this fish, and as Mr. Pennant, in his 

 British Zoology, wishes a farther account may be given of it, I thought it not 

 unworthy of the Society's notice. The fish itself was stuffed, and is now at the 

 British Museum.* 



XXX F. A Description of the Exocoetus Folitans; or Flying Fish. By Thomas 

 Brown, Surgeon, near Glasgow, p. 791- 

 This specimen was of the middling size, about 9 inches long, and full 4 

 round at the thickest part. From the largeness of the head, and the body being 

 neither prominent above nor on the sides, the eyes are situated in such a manner 

 as to discover their danger or prey almost all around them ; but when they are 



* It is well represented in the splendid Ichthyolog)' of Dr. Bloch. pi. 8(>. 



