VEETEBKATES. 385 



gently arched basal margin, which forms an acute angle with the broad 

 basal area, but without a trace of coronal folds, subcrescent-shaped in 

 outline; concave crown-face originally presenting a broad, regular len- 

 ticular outline, but in the present condition the crest is very gently 

 arched, while the basal border is more strongly arched downward and 

 moderately produced beyond the basal region to which it is sharply 

 inbeveled, the extremities somewhat more abruptly curved upward to 

 the lateral angles, and bordered by a strong coronal belt composed of 

 three or more well-defined parallel imbrications, which gradually narrow 

 on approaching the extremities, the superior region gently depressed or 

 nearly plane, smooth and polished, or with vertical striae above the 

 basal band. The base is relatively small, low, lateral extent consider- 

 ably less than the crown, well-defined from the broad basal area beneath 

 the convex crown-face, inferior surface more or less distinctly defined, 

 or rounded, beveled in nearly the same horizontal plane as the crown, 

 and irregularly divided into six, more or less, radicles, coarsely rough- 

 ened. A tooth .70 inch in lateral diameter, measures in transverse 

 diameter .26 inch, depth of base beneath the concave crown-face about 

 .07, lateral diameter about .45 inch across the lateral angles. 



Mr. Speingeb has obtained another representative of the present 

 form, in the same horizon at Keokuk, Iowa, represented in PI. X[, fig. 

 23, which shows a very worn tooth from the inferior side, the coronal 

 region having been even more reduced from attrition than the former 

 example, but exhibiting the same abbreviated or transversely widened 

 outline. These teeth are intimately allied to the Upper Burlington 

 form described by Messrs. Newbeeey and Woethen under the name 

 P. porosus, from which they may be distinguished by their shorter and 

 more lenticular outline, narrower and more strongly downward arched 

 basal belt. In the latter respect they bear some resemblance to P. 

 ampins of the St. Louis; the latter form, however, should it prove to be 

 distinct from P. Littoni, N". and W., is less symmetrical in outline, and 

 the concavity of the concave crown-face is much greater than obtains 

 in the teeth under consideration. 



The form is dedicated to Dr. G-. A. Williams, to whom we are indeb- 

 ted for the use of valuable material from the Keokuk and Warsaw beds 

 at Boonville. 



Position and locality : Upper fish-bed horizon of the Keokuk lime- 

 stone ; Boonville, Missouri, and Keokuk, Iowa. 



