26 E. B. BRANSON 



specimens of the teeth of Sandalodus and Deltodus have been studied, 

 and one fundamental difference, perhaps of family rank, seems to 

 distinguish one genus from the other. This difference is in the 

 number of teeth to each ramus of the jaw, Sandalodus having only 

 one tooth to each ramus and Deltodus having three. Only the actual 

 finding of the teeth in place can prove this conclusion beyond all 

 question, but the evidence in hand makes it seem more than probable. 

 In all cochliodonts, whose full dentition is known to have more than 

 one tooth upon each ramus of the jaw, the posterior teeth have their 

 antero-lateral margins modified for articulation with other teeth. 

 The teeth of Sandalodus have no articular edge and show no sign 

 of other teeth having been in contact with them. No teeth of proper 

 shape and size to fit the large plates of Sandalodus have been observed 

 during the present investigation. St. John and Worthen figure and 

 describe 1 what they call median mandibular teeth of Sandalodus 

 laevissimus, but, judging from the figures, the teeth are far too much 

 enrolled to fit the large plates of S. laevissimus. Furthermore, if 

 anterior teeth were present, they should be preserved in as great 

 abundance as the so-called posterior teeth, but, aside from those 

 figured by St. John and Worthen, none of the kind are known, while 

 the posterior teeth are rather common. In the Burlington limestone, 

 where the teeth of Deltodus spatulatus and Sandalodus occidentalis 

 are about equally common, the anterior teeth of D. spatulatus are 

 numerous, though usually fragmentary; but no teeth that fit the 

 large plates of S. occidentalis have been found. In regard to the 

 dentition of Sandalodus, Davis says: "It does not appear probable 

 that there was more than one tooth to each ramus of the jaw." 2 

 Davis believes that the mandibular teeth of Sandalodus differ con- 

 siderably from the maxillary teeth, but in a study of all the specimens 

 of this genus in Walker Museum it has proved impossible to dis- 

 tinguish mandibular from maxillary teeth, and this is true also of 

 Deltodus. 



There can be little doubt that Deltodus had three teeth on each 

 ramus of the jaw. Owen has shown 3 that in the complete dentition 



' Op. tit., Vol. VII, p. 1 66, Plate XII, Figs. 8 and 9. 



2 Scientific Transactions of Royal Dublin Society, Vol. I (1883), Series III, p. 436, 



3 Geological Magazine, Vol. IV (1867), p. 60, Plates III and IV. 



