B. Smith— Note on the Miocene Drum Fish. 279 



tion just which one of these Miocene horizons furnished the 

 fossil. It is probable, however, that the type came from the 

 St. Mary's formation, for this is the one in which the species 

 has been found in Maryland. 



The very meager fossil material* at the writer's disposal is 

 hardly sufficient to illustrate any evolutional changes which 

 may have taken place in the genus during its geological range. 

 It is, therefore, to be regretted that we have, as yet, no means 

 of checking the probable phylogeny which is suggested by an 

 ontogenetic series of the pharyngeals of the recent P. cromis. 

 It is evident from such a series that this peculiar type of crush- 

 ing apparatus was developed by (1) the enlargement of the 

 second pair of upper plates, (2) a progressive change from the 

 inner margins outward from denticles to crushing teeth in both 

 upper and lower plates, and (3) the fusion of the two lower 

 plates. The enlargement of the second pair of upper pharyn- 

 geals was accompanied by a corresponding reduction of the 

 first and third pairs together with a degeneration of their 

 denticles. In both the second pair of upper plates and in the 

 fused lower plates the young examples of this species exhibit 

 every gradation between sharp denticle and blunt crushing 

 tooth (figs. 3, 7). In the young the clenticled area is relatively 

 quite large, while in the old individuals a few blunt denticles 

 only are found on the outer margins of the upper and on the 

 postero-lateral angles of the lower fused plates (figs. 4, 8). 



In conclusion, we can say that the peculiar crushing 

 apparatus in the pharynx of Pogonias is, in all probability, the 

 product of a series of evolutional changes which in a general 

 way corresponded to those shown in the ontogeny of P. cromis, 

 and it is also reasonable to suppose that the Pogonias stock, 

 which had acquired its generic characters as far back as the 

 Miocene, was preceded in time by forms the pharyngeals of 

 which had reached a stage of specialization somewhat similar 

 to that exhibited by Microjoogon undulatus. Though 

 recognizing fully the scantiness of the data, it is believed that 

 the morphological gradations exhibited by the lower pharyn- 

 geals of Cynoscion, Micropogon, and Pogonias (PL I, figs. 

 1, 2, 3, 4), and by the upper pharyngeals (PL I, figs. 5, 6, 7, 8) 

 of the same three genera, represent an approximation to the 

 phvlogenetic changes which have culminated in the crush- 

 ing apparatus of Pogonias. 



Acknowledgments are due to Prof. Bashford Dean of the 

 American Museum of Natural History for the loan of type 

 material and to Mrs. Ethel Ostrander Smith for the careful 

 execution of the drawings here reproduced. 



- I have not yet been able to locate Leidy's specimens from the Ashley 

 Eiver Sands. 



