SCIUEOMORPHA. 823 



preserved in any of my specimens. The premaxillary bone is continued 

 upwards and backwards to the frontal, ceasing with the posterior extremity 

 of the nasal. Of the superior maxillary teeth the first and third are equal, 

 while the second is a little larger. The fourth has about three-fourths the 

 linear dimensions of the third. The outlines of all are, in horizontal section, 

 quadrate with rounded angles. The incisors are much compressed, and the 

 anterior face of each is strongly and equally convex. The inner angle is pro- 

 nounced, while the external is rounded. The enamel is smooth, without 

 groove or keel, and does not lap over on the inner side. It extends a short 

 distance on the inner side, forming a narrow band. 



The mandibular ramus is of rather slender proportions, much as in 

 Hesperomys leucopus. The symphyseal portion leaves the inferior border at 

 an angle of 135°, not being continuous as in Sciurus relictus, nor so steep 

 as in Eumys elegans. The inferior border is nearly straight, -with a slight 

 contraction below the last molar. The grinding surfaces of the molars form 

 a plane which rises a little forwards. The pterygoid fossa is deep, and is 

 bounded below by a thickened continuation of the inferior border. The 

 ascending ramus commences opposite to the posterior end of the third molar, 

 and its anterior border is quite oblique. The coronoid process is a rounded 

 laminar projection, and is quite low. A groove separates its base and that 

 of the condylar portion from the tuberosity which contains the papilla of 

 the inferior incisor tooth. The masseteric fossa is well defined by borders, 

 which are not prominent, and which unite in an acute angle below the 

 middle of the first molar, above the middle of the side of the ramus. The 

 foramen mentale is opposite the middle of the diastema and close to the supe- 

 rior plane. 



The inferior incisor is compressed like the corresponding superior tooth. 

 The front is symmetrically convex, but rounds into the outer side, while it 

 is separated from the inner by an angle. The enamel does not fold on to 

 the inner side, but covers about one-third of the outer side, as seen in pro- 

 file view. A feature of this tooth, where it differs from the corresponding 

 one of the upper jaw, is seen along the line where the anterior passes into 

 the external surface. Here is a delicate groove, which is bounded on the 

 outer side by an equally delicate thread-like ridge. In some specimens a 



