Affinities of the Cretaceous Fish Protos])hyra2na. 511 



sf)ht/r(P7ut, so in llypsocormus the premaxilla bears a tew very 

 lai<i:e teeth, tlie inaxilhi iiaviiii^ smaller and more numerous 

 teeth. 



(2) Cheek-plates. — Besides the large postorbital cheek- 

 plates in rrotosphi/nrna Felix also notes {loc. cit. p. 282) 

 some comparatively small secondary jtostorbitals forming the 

 actual liinder border of the orbit. Exactly the same arrange- 

 ment is observed in Ilupsocornnis (Brit. Mus. nos. P. GOll, 

 V. G917), as also in the allied genus Pacht/cormus * . 



(3) Mandible. — The mandibular symphysis is similarly 

 constituted in the two genera under comparison, the stout 

 (anterior) splenials entering the symjihysis, rapidly tapering 

 behind, and each bearing one or two very large teeth in 

 addition to the smaller teeth. In both genera also the ante- 

 rior end of the tooth-bearing margin of the dcntary bone 

 curves downwards and is provided with about three large 

 teeth pointing forwards. The ])resent writer has never 

 observed any evidence of a distinct presymphysial bone in 

 either genus. 



(4) Structure of the large Teeth. — Felix observes {loc. cit. 

 p. 289, pi. xiv. fig. 4) that, when viewed in transverse section, 

 the large teeth of Protosphyra^na exhibit a remarkably com- 

 plex structure. They are, in fact, compound, showing a 

 number of distinct small pulp-cavities, each surrounded by its 

 own separate zone of vasodentinc. Precisely the same struc- 

 ture can be seen in a transverse section of a large tooth of 

 Hypsocormus Leedsi in the British JMuscum (no. P. 6914). 



(5) Branchiostegal Apparatus. — The large gular plate and 

 numerous broad branchiostegal rays shown by Felix in his 

 figure of Protosphyrcena {loc. cit. pi. xii. fig. 3) are exactly 

 similar to the corresponding plates in llypsocormus and Pachy- 

 cormusj and only approached among " Teleostei " in Elops 

 and its allies. 



(6) Pectoral Fins. — It is now proved f that the pectoral 

 fins of Protosphyrcena are the well-known fossils described 

 by Cope under the name of Pelecopderus \ -, and on comparing 

 these with the corresponding fins oi Hypsocormus as shown in 

 the British Museum (nos. P. 6011, 6917), it will be observed 

 that there is a very close general resemblance. The fin-rays 

 are unjointed except quite at the extremity, and they are all 



* H. E. Sauvage, " Note sur le Genre Pachycormus,^ Bull. Soc. Linn. 

 Normandie, [3] vol. vii. p. 144, pi. iv. (1883). 



t A. R. Crook, ralseoutoj^^r. vol. xxxix. p. 110. 



X E. D. Cope, •■ Vertebrata of the Cretaceous Formations of the West,' 

 p. 244 a (1875). 



