VEETEBEATES. 333 



extremities. This accessory branch is unmistakably firmly attached to 

 the parent body, there being not the faintest trace of suture or other 

 indication of its independent origin. The specimen is unique in this 

 respect, though recalling the appearance of the tooth shown in fig. 33; 

 but no similar detached teeth have as yet been found — the oblique 

 direction of the cusps of the accessory branch, which appear nearly at 

 right angles to the direction of those in the principal plate, would at 

 once attract the attention in case they are hereafter discovered. 



A specimeu of the form under consideration, in which a portiou of 

 oue of the lateral faces has been broken away, reveals something of the 

 internal structure, or sufficient to show that in the dentine portion of 

 the tooth the individuality of the cusps is maintained nearly to the 

 inferior plane of the base, presenting a segmented condition, which is 

 quite concealed by the external coating of enamel in the crown and the 

 density acquired by the exposed portion of the base. Were these den- 

 tal plates always found in the symmetrical condition of the specimen, 

 Fig. 37, the question might arise whether they are referable to the den- 

 tal apparatus of the fish, but pertain to the dorsal defense and akin to 

 the segmented defensive spine originally described by Dr. Leidy under 

 the generic name Edentus, which they also somewhat intimately resemble 

 in general shape. 



STEMMATODITS SYJVIMETRTCUS. 

 PI. 8, Kg. 28. 



A form, of which we have seen very few examples, represented by 

 very small teeth, having the lateral diameter equal to or exceeding that 

 from front to rear, and nearly symmetrical in shape. The basal region 

 is considerably produced laterally, beveled above to the lateral edges, 

 which are sharply rounded and rapidly converge towards the anterior 

 extremity from about the middle, whence posteriorly they are nearly 

 parallel or but slightly diverge; in front the superior borders are marked 

 by a pair of lateral and median folds, the inferior surface presenting an 

 elliptical outline, moderately excavated and delined by the strong, 

 obtuse anterior and posterior border, sometimes arched downward lat- 

 erally, as shown in the specimen figured. The coronal region presents 

 two rows of cusps, which gradually diverge posteriorly, the cusps in the 

 respective rows irregularly alternating, and regularly or irregularly 

 increasing in size posteriorly — the specimen figured shows five and six 

 in each respective row, depressed, the posterior ones strongly produced 

 beyond the basal line ; the cusps are moderately compressed antero- 

 jjosteriorly, sublenticular in trausverse section, with sharp lateral angles, 

 which rapidly converge towards the sharply rounded apex, the anterior 



