200 ANNALS NEW YORK ACADEMY OF SCIENCES 



the teeth but m^ (right), and with the nasals and the posterior right side of 

 the cranium broken away. 



DESCKIPTION" 



Skull (Plate XIII, Figs. 1-3; Plate XIV, Figs. 1-4).— The skull is 

 essentially hystricomorph in general outlines with eight molar teeth and 

 large anteorbital fenestrse or passages for the masseter. The outline of 

 the skull above is somewhat similar to that of Mijocastor, flat-topped, with 

 nasals widening anteriorly, the greatest width of the skull just posterior 

 to the zygomatic process of the maxillary, a short sagittal crest, and a 

 pinched-in occipital region. The incisive foramina are small and set in a 

 deep narrow excavation in the palate. The tooth rows are divergent an- 

 teriorly and the post -palatal notch reaches to about the middle of the last 

 molar. The bullae are large and compressed laterally. An anterior por- 

 tion of a lower jaw, probably to be associated with the type skull, indi- 

 cates a deep ramus, an extensive symphysis and mandibles flaring pos- 

 teriorly from the symphysis. 



Dentition (Plate XIV, Fig. 2).- — The teeth present the most striking 

 characters. The incisors, tAvo in the upper and two in the lower jaw, are 

 long, curved and rather slender in proportion to the size of the skull. 

 The upper incisors show no striations, but the lower incisor has two well 

 defined grooves running the full length of the tooth and showing on the 

 cutting edge. The incisors are deeper antero-posteriorly than l)road lat- 

 erally, and in the lower jaw are noticeably flattened on the inner side 

 where each tooth meets its fellow of the opposing mandible. 



The molar teeth, four in each jaw and all of nearly equal size, are made 

 up of a succession of thin enamel plates, some of which are slightly 

 curved, alternating with bands of dentine. The enamel plates run com- 

 pletely through the tooth from side to side and their edges may be seen 

 laterally, as there is no encircling wall of enamel. There are five of these 

 plates in all of the upper molars and in addition the last two molars have 

 a vestige of a sixth plate. The only lower tooth in position, the first of 

 the molar series, has five plates, and this condition prevails in a numl)er 

 of uncorrelated teeth, leading me to expect the lower teeth to closely re- 

 semble the upper in respect to the number of plates. The upper pre- 

 molar is subtriangular in section, the three molars are quadrangular. In 

 all the molars, both upper and lower, the plates are set at a 23ronounced 

 angle to the line of the tooth row. The upper molars are set into their 

 alveoli at an angle that makes each row of teeth flare outward from the 

 other. Loose teeth show that this is due to a progressive curve in each 

 molar, beginning Avith the premolar. The curve to m^ is quite extreme. 



