AND AVES OF NORTH AMERICA. 101 



the posterior catting edge being directed outwards. The anterior alveolus is shallower than the second, and this 

 shallower than the third, which gives an oblique slope to the fractured margin of the bone, and suggests the applica- 

 tion of another skeletal piece. This I suppose to be the premaxillary, as the bone is externally too Hat to permit the 

 median premaxillary suture to occupy that position. The upper portion may be related to the margin of the nares. 

 A series of five foramina extends along the outer face of the bone opposite the middle of the depth of the alveola;. 

 The alveola; are directed more anteriorly from behind forwards. 



Linen. 

 Depth of alveolus, 34 



Length crown of successional tooth, 25 



Length piece embracing four alveola}, 01 



Mandible. — One portion from the anterior part of the ramus. The latter measure three inches in depth from the 

 outer alveolar border, which is a little more elevated than the internal, and 1.5 in. in thickness at the fractured edge. 

 A longitudinal series of vascular foramina extends along the middle of the external face. The teeth are implanted 

 in deep alveola?, and had transversely oval compressed fangs; the sections of the crowns of teeth from different 

 portions of the ramus differ. Two from the anterior region are considerably recurved, the concave or posterior edge 

 deticulate to the base of the enamel, the anterior aspect minutely serrate, two fifths the length from the tip. Section 

 at this point lenticular, lower down the anterior face becomes broader and rounded, giving a rounded cuneiform 

 section. Throughout, one face is more convex than the other. A young posterior tooth yet in the alveolus (no. 3) 

 is less recurved, subacute, and of more lenticular section, having both edges denticulate to the base of the enamel. 

 Fangs hollow, the pulp cavity capacious but rapidly diminishing and short; the cast sulphide of iron and marl. 



Inches. 



No. 1; total length (fang broken), 2.33 



length of enamel, 1 . 83 



width below, .833 



anterior diameter, .438 



No. 2; length of crown (tip restored), 1.875 

 anterior diameter, .5 



No. 3; length of crown, 2.125 

 width at base, .688 



Larger teeth are indicated by fragments. The development of the teeth has apparently proceeded as in Megalo- 

 saurus. The development of the dental papilla takes place within a niche of the alveolus, between it and the inner 

 mandibular or maxillary wall. Small serate casps are found in this position beneath but a thin stratum of bone. In 

 one situation a second successional tooth occupies a position between the primary cusp and the functional tooth, and 

 is about intermediate in size between them. These successional teeth then increasing in size, by a horizontal move- 

 ment, transverse to the cranial axis, place themselves close to the fangs of the functional teeth, into whose places 

 they gradually rise. An absorption of the dental wall probably prepares the older tooth for shedding, at which time 

 the apex of the successional tooth is ready for use.* 



Vertebra. — No cervical or dorsal vertebrae were preserved ; we have only as yet sacrals, and numerous caudals. 

 All are much constricted medially, or hour-glass shaped, the centrum cylindrical in section throughout in most of the 

 caudals, the anterior of the latter and the lumbars of deeper vertical than transverse diameter throughout. The 

 articular surfaces are moderately shallow biconcave in all, most strongly in the subproximial caudals. The neural 

 arches attached by permanent suture, and inferior surfaces for articulation of chevron bones. The caudals offer 

 indication of neural spines ; their traces are on the majority low, and of considerable longitudinal extent. Articular 



*Deslongchamps figures a tooth as doubtfully belonging to Poecilopleuruni. It resembles that of a Crocodilian, and probably belongs to a species of thai 

 subclass. He states that Megalosaurus-like teeth occur in the strata in which Poecilopleuruni was found. There is now much reason to believe that the latter 

 are the true teeth of the genus in question. 



AMERI. PHILOSO. SOC. — VOL. XIV. 26 



