ACANTHTDIUM PUSILLUM. 39 



especially the Rays and Skates, deposit those curious yellow horny cases, 

 like a handbarrow or butcher's tray, often called, on the English coasts. 

 Sea-purses, or Skates"'-eggs. 



Most of the Selachidee (Sharks and Rays), observed cursorily, appear to 

 the naked eye to be merely granular or rough, and devoid of true imbri- 

 cated scales. But, when examined with a lens, the roughness of the skin 

 is found with few exceptions to be caused by minute and elegantly formed 

 scales ; anomalous in form and structure, but disposed quincuncially like 

 those of ordinary fishes. Many of the Rays, and some few Sharks, are 

 furnished also with large bony scattered dermal tubercles or plates. The 

 substance called Shagreen, or by the French Chagrin,* is prepared from 

 the coarse-grained skins of certain species of the Shark or Ray : and the 

 rough skins of other sorts are used by cabinet-makers and other artisans for 

 polishing their manufactures. 



The Sharks were by Linneeus all united in a single genus Squalus ; 

 which the accession of new species, and the application of a stricter critical 

 analysis, have obliged later naturalists to raise into the rank of a tribe 

 or family Squalidfe, distinguished from the Rays or Skates (Raiidtt), 

 by the elongated, more or less cylindric form of body, by the fins in figure, 

 size, position, and proportion, corresponding with the ordinary fishes, by 

 the arrangement of the branchial openings on the sides of the neck, and by 

 the lateral position of the eyes. The two families agree with the Sturgeons 

 {Sturionido') anatomically in having the c^eca united into one mass, form- 

 ing a sort of pancreas or sweetbread, -f* and the intestine furnished with 

 a curious internal, generally spiral :j: appendage, like the worm of a female 

 or hollow screw : and they accord with each other in the distinction of the 

 sexes by the presence of a pointed cartilaginous appendage, called a clasper, 

 attached to the inner margin of each ventral fin, characterising the male fish 

 fi-om its earliest stage ; and in the frequent presence in both sexes of a 

 temporal orifice or breathing hole (spiracle, or in French eveyit) behind each 

 eye, destined, perhaps, in certain positions of the fish, in which the mouth 

 is closed, to admit the water to the branchiae, or to allow of its expulsion 

 from the mouth, when occupied in holding or in masticating food. 



* These words seem to be derived from the Italian. Willughby says, that Sagree (Ital. Sagri) 

 is the common name for Spinax niger, Cuv. with the Ligurians or Genevese : and hence its application 

 under different forms of orthography to the skins of other Sharks. 



■f See under Lampris luuta, supra p. 33. 



X In one of tlie Hammer-fishes {Zygesna fades, Val.) and in another Shark of doubtful genus 

 {Galeus? thalassinus, Val.), M. Duvernoy has observed this internal appendage to be a membrane at- 

 tached longitudiually, instead of spirally, and rolled up cylindrically on itself. He considers it as 

 constituting in these instances a kind of internal mesentery. An analogous structure exists also in 

 the Lampreys. See Ann. des Sciences Nat. 2d Serie, iii. 274. tt. 10, II A. 



In the common Hammer-fish, the German naturalist Meckel had previously made the same dis- 

 covery. 



