482 PROCEEDINGS OF THE NA TIONAL MUSEUM. vol. xxxn. 



frontal suture I have already described. A suture quite as evident 

 on each side runs obliquely outward from the hind end of the frontals 

 or nasals, and then turns downward, about as figured by Owen for 

 Plesiosaurus. The postf rental, as thus defined, joins the parietal 

 and touches the epipterygoid internally, the frontal anteriorly, and 

 the postorbital exteriorly. The postorbital articulates with the pre- 

 frontal anteriorly, the postfrontal on the inner side, and, by its 

 anterior angle, the so-called frontal; and the jugal exteriorly. The 

 two bones, seen from behind, present a broad, nearly vertical wall, 

 deflected somewhat anteriorly below, and ending in a thin, sharp, 

 nearly horizontal margin, continued from the epipterygoid notch to 

 the jugal. The orbital border of the postorbital is thinned, some- 

 what serrated, and concave. The temporal border above is sharp 

 and angular, curving downward to terminate in the thin upper margin 

 of the zygoma. The bone outwardly is massive and strong, ending 

 in a horizontal suture, which is nearly continuous with the lower border 

 of the orbit and the upper front border of the zygoma. 



Jugals. — The jugal differs considerably from that of other forms 

 of plesiosaurs known to me. The sutures distinguisliing it from the 

 postorbital, lachrymal, and maxilla are very clear, as I have described 

 and figured them. That uniting it with the squamosal is doubtfid. 

 On the left side the bone has been separated very cleanly from the 

 matrix, and is in a beautifully uncUstorted condition. A little back 

 of the liind border of the postorbital there are, near the middle of the 

 jugal, the orifices of two or three malar canals. These canals are 

 very characteristic of the plesiosaurs, and usually open near the 

 squamoso-jugal suture, but there is not the slightest indication of 

 such a suture here. These canals, piercing the jugal, enter the orbit 

 near its lower posterior corner. In the orbit the jugal turns inward 

 for a considerable distance, forming a bowl-like floor posteriorly; its 

 inner border I can not trace. 



Describing the zygoma as a whole, it has a somewhat tliickened 

 upper border in front, thimied below. The arcade chminishes rapidly 

 in width, chiefly at the expense of the lower part, to beyond its mid- 

 dle, where its width is less than one inch, and the bone is tliin and 

 weak. At this place the arch, on both sides, shows an oblique fi'ac- 

 ture, which may, possibly, represent the squamosal suture, though I 

 am very doubtful. I have indicated this possible suture by dotted 

 lines in the drawings. The squamosal beliind broadens to a width of 

 about two and a half inches where it joins the quadrate, and is thicker 

 here, the upper border ascending rapidly; the lower border is concave. 

 The zygoma is very remarkable for its attenuation posteriorly, leaving 

 a large open space above the posterior part of the mandible in front 

 of the articulation. I can conceive of the complete erosion of the bar 

 here, as occurs in some turtles, leaving the temporal vacuity broadly 



