in the Fish Gallery of the Indian Museum. 85 



Indo-Pacific. Some of the Trygons grow to an enor- 

 mous size. 



Family VI. 3fi/liobatidce [Case 33]. 



The Eagle-rays or Sea-devils chiefly differ from the 

 Trygons in having a thicker disk and a slightly differ- 

 ent arrangement of the pectoral fins, which are more 

 extended laterally and less extended forwards. 



In their mode of life they much resemble the Trygons, 

 and have a pavement-like arrangement of crushing-teeth 

 even more perfect than that of the Trygons. Some of 

 them resemble the Trygons in their mode of bringing 

 forth their young. Some of them grow to an enormous 

 size. All the four Indian genera of Eagle-rays also 

 occur in the Mediterranean and Atlantic. 



Order II. HOLOCEPHALA [Cases 30-32]. 



Of all the members of the subclass Chondropterygii, 

 the Holocephala, or Chimaeras, make the nearest approach 

 to the Ganoids. They differ from all other members of 

 their subclass, and resemble the Ganoids and their des- 

 cendants, in having a gill-cover and so only a single 

 external gill-opening on each side. But the gill-cover 

 is a rudimentary one, and merely covers the four exter- 

 nal gill-clefts, which resemble those of sharks : it does 

 not cover a gill-chamber in which the gills lie free. Ex- 

 cept in this respect and in certain skeletal characters, 

 the Chimaeras agree with the Sharks. The males have 

 a singular erectile appendage on top of the head. 



No actual specimens of Chimcera and Callorhynchus 

 (the two genera that now constitute the Order) have been 

 taken in Indian seas, but their empty egg-capsules have 

 been dredged in the Bay of Bengal between 400 and 600 

 fathoms, so that specimens may be discovered any day. 



