1869.] 311 [Cope. 



the bone there are four longitudinal rows of teeth, anteriorly five or 

 six. A successional tooth extracted had a crown subtrigonal in out- 

 line, the surface projecting strongly. The successional teeth have 

 evidently passed entirely through the bone from below, absorbing the 

 ostein above them, and on reaching the surface have been strength- 

 ened by the ossification of the pulp below them, which has thus 

 closed the opening already made. 



Inches. 



Length of upper pharyngeal bone 1.87 



Long, diameter of tooth, first row 3 



" " " second row ; .18 



Obtained by my friend, Oliver N. Bryan, from the Miocene chfis 

 of Nomini, Westmoreland Co., Virginia. 



Phacodus irregularis Cope, gen. et. sp. nov. 



Char. gen. Teeth fusiform, irregularly and closely crowded on the 

 surface of an elongate semidiscoid bone of possibly the hyoid appara- 

 tus. Masticatory surface moderately convex ; crown abruptly con- 

 tracted below into a short root, which presents a very small orifice for 

 the admission of the nutrient vessels, etc. The teeth have thus 

 somewhat the shape of an onion inverted. The pulp cavity is large. 

 The superficial layer of the crown is very thin : its structure has not 

 been definitely ascertained, but its punctate appearance resembles 

 that of a worn surface of vaso-dentine. 



The successional teeth are very abundant, and closely placed; they 

 appear to rise through the spongy tissue of the bone without refer- 

 ence to any definite line of succession or superposition. Those of the 

 inferior sex-ies, visible on the under surface of the bone, have an 

 average larger size than those of the upper surface which are in use. 



This genus is allied to the Pisodus of Owen (Odontography, p. 

 138), and like it, is of uncertain affinities. I have regarded it as 

 distinct from the latter, since Owen says, in it the crowns of the teeth 

 "are extremely dense and hard." In Pliacodus the masticatory 

 layer is very thin and penetrated by minute orifices, and cannot 

 have been subject to much attrition OAving to its lack of hardness. 



Char, specif. The teeth, though irregularly arranged, are for short 

 distances in longitudinal lines. They are transversely ovate and 

 closely packed, or Avith slight intervals. Those at the outer and inner 

 margins of the bone are considerably smaller than the median, and 

 more rounded. The crowns of the successional teeth are flattened, 

 as well as those in use. The median teeth number five in a half inch; 

 the lateral seven in the same length. The surface of the root is 



