276 B. Smith- — Note on the Miocene Drum Fish. 



adapted for either cutting or crushing. The most casual study 

 of such a series suggests that the crushing type has resulted 

 from a modification of the plate, which is covered with 

 denticles. For this reason it is advisable to consider the 

 pharyngeals of some scisenoid genus which is primitive in this 

 respect {Cynoscion) and compare them with those of a less 

 primitive form (Micropogon), and finally with those of a highly 

 specialized form {Pogonias). The species which have been 

 selected for this purpose are Cynoscion nebulosus (C. and V.), 

 Micropogon undulatus (L.) and Pogonias cromis (L.). 



The Lower Pharyngeal Plates. — In Cynoscion nebulosus 

 the lower pharyngeals differ little from those of the normal 

 teleost fish. They represent the inward plate-like expansions 

 from the rudimentary fifth eerato-branchial, are not fused but 

 remain distinct (right and left), and are covered by sharp 

 backwardly curved denticles which are largest along the inner 

 (median) anterior margin of each plate. In Micropogon 

 undulatus the same general shape prevails but each plate is 

 proportionately broader and heavier. When, however, the 

 dental elements of the plates are examined we find a marked 

 change from the condition observed in Cynoscion, for in 

 Micropogon the denticles are much fewer, and though still 

 small and sharp on the lateral (outside) and postero-lateral 

 regions they have become large and blunted on the anterior 

 inner (median) border. If now we extend our comparison to 

 Pogonias cromis we find that the inwardly directed plate- 

 like portion of each fifth cerato-branchial has expanded until 

 it meets its fellow on the opposite side and is firmly united by 

 suture with it. In addition each bone has developed on its 

 under surface a prominent process directed downward, for- 

 ward, and outward for the attachment of the powerful muscles 

 needed in the operation of the fused plates. In conjunction 

 with this, fusion and strengthening the functional surface has 

 developed bean-like crushing teeth. These are largest along 

 the median (inner) margin of each one of the plates and 

 decrease in size forward, backward, and outward. A few 

 sharp denticles are still retained on the postero-lateral margins 

 of each member, but the transition from sharp denticles to 

 crushing elements can only be well seen in young examples 

 of the species (fig. 3). 



The Upper Pharyngeal Plates. — The upper pharyngeal 

 plates of Cynoscion nebulosus exhibit no marked divergence 

 from the normal teleost type. There are three well-marked upper 

 plates on each side all covered with sharp backwardly curved 

 denticles. The anterior plates (right and left) are narrow, 

 lie forward and outside of the second pair of plates, and are 

 directed forward and inward. The second pair of plates are 



