i7'S R. E. Lloyd : Neiv species of Eagle-Rays. [Vol. II, 



cephalic fins. The skeleton of these fins^ as in the other members 

 of the MyliobalidcB , is directly continuous with the skeleton of the 

 pectoral fins. The actual brain case is a very insignificant part of 

 the cranium^ being represented by a dome-shaped box measuring 

 only 13 cms. in breadth, situated close to the condyles. 



With the exception of the small portion which lodges the brain, 

 this cranial lamina has a uniform thickness of half an inch in the 

 dried state. It terminates laterally in simple margins, hence the 

 cranium appears to be devoid of true orbits. At one point, on 

 either side, the dry cartilage composing these margins is prolonged 

 outwards towards the eyes as two slender shrivelled tubes which 

 doubtless contained the optic nerves. Owing to decay it was im- 

 possible to ascertain the point at which the ocular muscles were at- 

 tached to the cranium ; this point would have indicated the site of 

 the orbit. 



The eyes were well preserved for, as in many other large elas- 

 mobranch fishes, the sclerotic coat was composed of thick tough car- 

 tilage ; in this case the cartilage composing the back of the eyeball 

 was more than half an inch in thickness ; it was indeed so mas- 

 sively developed that on first examination it was thought to be the 

 orbit itself which had been attached to the cranial margin by the 

 slender tubular prolongation beforementioned. This misunderstand- 

 ing was corrected by finding traces of the tendinous insertions of the 

 ocular muscles attached to the outer surface of the globe. 



The jaws and their suspensory apparatus were of the type 

 common to the order. The hyomandibular is laminate in form and 

 is firmly attached at its upper (or inner) end to the cranium close 

 to the occipital condyle of the same side; it also receives additional 

 support by being, as it were, wrapped round the posterior margin 

 of the cranial plate. Its lower (or outer) end supports the jaws and 

 hyoid. The upper and lower jaw differ remarkably in appearance. 



The upper jaw is a straight slender bar, no thicker than a 

 man's thumb, attached at either end to the hyomandibulars. The 

 lower jaw, which has, of course, the same attachments, is a massive 

 plank-like structure measuring 12 cms. in depth ; one surface of 

 this looks upwards and forwards and bears the curious ribbon-like 

 band of teeth which are detachable with the skin. 



The lower edge of the mandible forms a prominent ridge sharply 

 defining the oral face from the ventral surface ; in the same way 

 the anterior margin of the cranial lamina, which forms an open 

 curve, sharply separates the oral face from the dorsal surface. 



The skeleton, which carries the great pectoral fins on either side, 

 is prolonged forwards beneath the spatulate processes of the 

 cranium, to render support to the cephalic fins; beneath these 

 processes it is united to the cranium itself by a cartilaginous bar 

 which is fixed to the cranium just outside the nasal fossa (point X , 

 fig. I, pi. x). 



In order that a better understanding of the cranium might be 

 arrived at, the skull of Aetohatis, a common genus belonging to the 

 Afy/»o6a^iwa, was cleaned and examined. -.-,.-'-- ..- 



