20 WEALDEN AND PURBECK FOSSIL FISHES. 



irregular wrinkles wliicli are directed chiefly along the longer (transverse) axis of 

 the tooth. Seen from below (fig. 1 <i) the crown clearly overhangs the root on all 

 borders. In anterior view (fig. 1 !>) the vertical Avrinkling is conspicuous, and the 

 crown is seen to be deepest at the Avider end. In posterior view (fig. 1 c) the 

 sharp margin of the oral surface forms a prominent ledge over the comparatively 

 smooth, concave posterior face. The narrower end (fig. 1 d) is gently rounded, 

 but marked by two well-separated small pressure-scars. The bevelled Avider end 

 (fig. 1 e) is also marked by two larger pressure-scars. A second tooth from Brook 

 (PI. V, fig. 2) is very strongly Avorn in its posterior half, and the Avorn surface is 

 widest in the middle with a nearly semicircular margin. One end of the tooth is 



Fig. \0. — Hylxohati.i prohlematica, g;cn. et sp. nov. ; vertical anteroposterior section of crown of tooth, 

 enlarged about 20 times. — Wealdon : Sevonoaks, Kent. Sedgwick Museum, Cambridge. 



again Avider than the other and more distinctly bevelled for contact Avith two teeth ; 

 and its rounded anterior border (fig. 2 a) exhibits the vertical wrinkling. On the 

 unAvorn part of the oral surface the irregular wrinkles are mainly in the direction 

 of the long axis of the tooth. A larger and more transversely-elongated tooth 

 from Sevenoaks (PI. V, fig. 3) displays well the vertical wrinkling of its anterior 

 border, l)ut the oral surface seems to have been AA'orn nearly smooth. One extensive 

 pressure-scar occurs at each lateral end of the tooth, and the specimen is broken 

 across to exhibit the transA^erse section (fig. 3 a). The microscopical structure of 

 this transverse section is shoAvn highly magnified in Text-fig. 10, Avhere the darkly- 

 stained enamel-layer (ganodentine) extends both over the upper oral surface and 

 over the posterior concave surface, while the ordinary dentine is traversed by 

 radiating and bifurcating vascular canals, which are bordered Avith canaliculi 

 throughout their length and terminate in a tuft of canaliculi beneath the ganodentine. 



