Extinct Selachian Asteracantlius. 337 



Five series of associated remains are of especial importance, 

 and form the basis of the descriptions given below. They 

 may be enumerated as follows, under Mr. Leeds's catalogue 

 numbers : — 



1. Two dorsal fin-spines, with two cephalic spines. 



2. Two fragmentary dorsal fin-spines, with one frag- 



mentary cephalic spine. 



3. One dorsal fin-spine, with twenty teeth. 



4. Two dorsal fin-spines, with numerous portions of car- 



tilage and ninety-seven teeth. 



5. Remains of the cartilages of the head, with eleven 



teeth. 



Nos. 4 and 5 afford some slight information concerning the 

 cartilages of the fish ; no. 1 makes known the singular cephalic 

 spines ; while some differences between both the dorsal fin- 

 spines and the teeth in nos. 3 and 4 render these also interesting 

 from a systematist's point of view. 



Cartilage. — The cartilages are only superficially calcified, 

 though the film of fine granular material is thick com- 

 pared with that of many living Selachians. Only one 

 fragment (no. 5) seems worthy of description and illustra- 

 tion, namely the right mandibular ramus, which is shown 

 from the outer aspect, of one third the natural size, in 

 PI. XII. fig. 1. This is much crushed and broken ; but it is 

 interesting as showing the extremely robust character of the 

 jaw. When complete the element must have had a length of 

 about 0*27 m., being obtusely rounded in front, measuring 

 about 0*085 in depth at the position occupied by the first 

 series of lateral teeth, and gradually widening behind, until it 

 attained a maximum depth of 0-14 at the condyle. On the 

 inner side there is distinct evidence of a thickening of the 

 cartilage of the lower margin immediately beneath the inferior 

 limit of the tooth-bearing membrane ; and on the outer side a 

 singular feature may be noticed, in the form of a protuberance 

 slightly in advance of a point halfway between the condyle 

 and the toterior extremity. Much of the external surface of 

 the cartilage has a coarsely fibrous appearance, and at the 

 point just mentioned several of these fibres curve upwards 

 and backwards from the inferior margin in front, producing a 

 large roughened boss [t) , in which their abrupt upper extre- 

 mities have the appearance of terminating. 1 have not been 

 able to discover a similar protuberance in any other Sela- 

 chian, living or extinct, and its exact meaning seems at 

 present inexplicable. That it is a normal feature is proved by 



