1871.] HTJLKE KIMMERIDGE ICHTHTOSAtTRI, 35 



maximum antero-posterior diameter of its root (nearly at the middle) 

 is about 8 lines. Tiie inner longitudinal line of this tooth is less 

 incurved than the outer one. 



Their much larger size at once separates the teeth of this Kim- 

 meridge species from those of the slender-snouted Liassic species (I. 

 longirostrls, I. tenuirostris, I. acutirostris), and from those of the 

 Kimmeridge J. entheJciodon, which I described last session*. Erom 

 the teeth of I. communis they differ notably in the relatively greater 

 ventricosity of the root of the latter. From the strongly fluted 

 tooth-root of this species, as also from the similarly marked tooth- 

 root of /. intermedius and of I. lonchiodon, the tooth -root of this 

 large Kimmeridge species is easily distinguishable by the comparative 

 faintness of its linear furrowing. The crown is much stouter than that 

 of I. lonchiodon, and its striation makes it impossible to mistake these 

 teeth for those of I. platyodon. They bear a close general resemblance 

 to the teeth of I. campijlodon ; but, from a comparison of them with a 

 good series of campylodon teeth in the British Museum, I find they 

 differ from these in the proportions of the root and crown, which 

 latter is longer and less stout in the Kimmeridge species ; but they 

 are better distinguished by the prolongation of the striae in the 

 form of lines of minute tubercles to the extreme end of the crown, 

 which in I. campylodon is smooth, the sculpturing ceasing at a short 

 distance from its apex. 



EXPLANATION OP PLATE IL 



Ichthyosauriaii Teeth from Kimmeridge. 



Figs. 1, 2, 3. One of the longer teeth, natural size: 1, outer surface; 2, side; 

 3, inner surface with germ-hollow. 

 „ 4. Root and small piece of the crown of one of the lesser teeth. 

 „ 5. An unworn crown, X 2, to show the sculpturing. 

 ,, 6, 7. A lesser and a longer tooth as bedded in matrix. 

 „ 8. Transverse section of the root of one of the longer teeth near the base. 



Discussion. 



Mr. Seelet did not consider that, in the main, the teeth of rep- 

 tilia afforded any criteria for specific determination. In the Cam- 

 bridge Greensaud, though there were five species of Ichthyosaurus, 

 possibly including a second genus, the teeth found were so closely 

 similar that it would have been impossible, from them only, to 

 identify more than one species. 



Mr. Boyd Dawkins recognized in the specimens exhibited by Mr. 

 Hulke a form of tooth he had found in the Kimmeridge beds of 

 Shotover, near Oxford, but which he had been hitherto unable to 

 attribute to any recognized species. He could not fully agree 

 with Mr. Seeley as to the absence of specific criteria in the teeth 

 of Saurians, as, from his own experience, he was inclined to attri- 

 bute some importance to their external sculpturing. 



* Quart. Journ. Gl-eol. Soc. vol. xxvii. p. 440. 



D 2 



