B. Smith — JVote on the Miocene Drum Fish. 277 



the largest of the three and the denticles which they bear on 

 their inner margins excel in size those of either the first or 

 third pair. The posterior pair of plates are larger than the 

 anterior pair but the denticles on their inner margins are very 

 weak. 



In Micropogon undtdatus the plates of the second pair have 

 increased in size at the expense of those of the first and third 

 pairs. It is true the third (posterior) pair are not greatly 

 reduced but their surfaces are covered with but small and 

 weak denticles. The plates of the first (anterior) pair are 

 much reduced in size and covered with weak denticles. The 

 plates of the second pair are large, the outer (lateral) margins 

 bear fairly sharp denticles while the inner (median) and cen- 

 tral regions cany denticles which are larger and more blunt. 



Turning now to the superior pharyngeals of Pogonias 

 cromis, we find that the second pair of plates is proportionately 

 much larger in size, while on the other hand the first and third 

 plates are proportionately much smaller, being in each case 

 narrow crescentic elements which are closely applied to the 

 curved anterior and posterior margins of each plate in the 

 second pair. These plates of the first and third pairs carry 

 weak degenerate denticles. In P. cromis it is the second pair 

 of plates which command our attention, for these are abnor- 

 mally large in size and the denticles have for the most part 

 been changed into blunt crushing elements. These bean-like 

 teeth are largest along the inner margin of each plate midway 

 between its anterior and posterior ends. From this region 

 (on each plate) the teeth become smaller as we pass forward, 

 backward, and outward. In addition as we go outward the 

 typical bean-like condition is less and less marked, the teeth 

 becoming gradually less and less blunt until we reach a small 

 patch on the extreme outer margin which still retains the 

 primitive sharp denticles. As might be expected, this transi- 

 tion between denticles on the one hand and crushing teeth on 

 the other is much more evident in the plates of young individ- 

 uals of Pogonias cromis / for the old examples of the species 

 have but a relatively small denticled area and only a few 

 transitional teeth (figs. 7 and 8). 



Comparison of the Pharyngeal Teeth of Pogonias cromis and 

 Pogonias midtidentatas. 



As stated above, the Miocene Pogonias multidentatus Cope 

 is known by but two specimens. The type is a right superior 

 pharyngeal from Xomini Cliffs, Westmoreland County, 

 Virginia, and the other specimen is a left superior from the 

 St. Mary's Formation of St. Mary's River, Maryland. Though 



Am. Jour. Sci. — Fourth Series, Vol. XXVIIL No. 165.— September, 1909. 

 19 



