RAYS. Ill 



Common Skate (R. batis), the Burton Skate (R. marginata), and 

 the Shagreen Skates. Some of these species, especially the Skates, 

 attain a considerable size, the disk measuring six and even seven 

 feet across. All are eatable, and some of them regularly brought 

 to market. Teeth are exhibited in Table-case C. 



The Tnjgonida, or Sting-Rays (Cases 43, 44), are as numerous [Case 44.] 

 as the Rays proper, but they inhabit tropical rather than temperate 

 seas. The species armed with a spine use it as a weapon of defence, 

 and the wounds inflicted by it are, to man, extremely painful, and 

 have frequently occasioned the loss of a limb. Some forms, 

 however (Urogymnus, Case 43), are devoid of that caudal weapon. 

 The genus Trygon is numerous in species, one of which [T. pasti- 

 naca) occurs on the south coast of England. Large specimens of 

 T. sephen and T. narnak (fig. 97) are exhibited on stands opposite 

 Case 42. 



The MyUobatidce (Case 44), also called Devil-fishes, Sea-devils, 

 or Eagle- Rays, are generally of large size, inhabiting temperate and 

 tropical seas. The tail is very long and slender. Some genera 

 {Cephaloptera, Dicerobatis) possess a pair of singular cephalic 

 processes, which generally project in a direction parallel to the 

 .longitudinal a^xis of the body, but are said to be flexible in the 

 living fish, and used for scooping food from the bottom and 

 conveying it to the mouth. Some of them, if not all, attain an 

 enormous size ; specimens weighing 1250 pounds, or 20 feet broad, 

 are on record. In the Myliobatina the dentition consists of 

 perfectly flat molars, forming a kind of mosaic pavement in both 

 the upper and lower jaws — a most perfect mechanical arrangement 

 for crushing alimentary substances. Examples of the dentition are 

 exhibited in Table-case C. 



CYCLOSTOMATA. (Case 44.) 



Their skeleton is cartilaginous and notochordal, without ribs 

 and without real jaws ; the skull is not separated from the vertebral 

 column. Limbs are absent, and the body is eel-like. The gills 

 are in the form of fixed sacs, without branchial arches, numbering 

 six or seven on each side. There is a single nasal aperture. The 



