BA.SKIXG SHAIIK. 



399 



backwards : tlic socoiul dorsal fin iiiutli smaller than the first, 

 rounded above, attached throughout half its base only, and 

 placed at two-thirds of the distance from the first dorsal to 

 the caudal fin ; the anal fin is still smaller than the second 

 dorsal, but of the same shape. From the line of the anal 

 fin to the base of the tail there is a strong and prominent 

 keel-like edge on each side ; and just in advance of the base 

 of the caudal fin, both above and below, is a groove, — that 

 underneath rather smaller than that above. The caudal fin 

 divided into two lobes, the upper one larger than the lower ; 

 the posterior edge of the caudal fin appears to become notch- 

 ed and abraded by age and use, and is frequently found un- 

 equal at its margin, and variable in shape. 



The vignette below represents the Arguius foliaceus of 

 Jurine ; another species of parasitic animal occasionally found 

 attached to fresh-water fishes. I have specimens that were 

 taken from the Pike and the Trout. The figure on the left- 

 hand represents the upper surface of a male : by the powers 

 of the microscope some of the vessels of the body are ren- 

 dered visible through the external tunic. The figure on the 

 right-hand represents the under surface of a female : the ova 

 are very conspicuous. The small figure between the two is 

 of the natural size. 



