92 MEMOIRS OF THE CARNEGIE MUSEUM 
Prefrontal ( prf.). —The shape of the prefrontal, or even the probable outlines, can- 
not be determined from the present specimens. On the right side of the skull per- 
taining to specimen No. 878 is a narrow portion forming the upper and forward 
boundary of the orbit extending down to meet the lachrymal in front. The narrow 
portion just cited is undoubtedly a part of the prefrontal as this is the position of 
this element in all fully figured Ichthyosaurian skulls. Although Baur” says, ‘‘ The 
lachrymal is free from the prefontal in Ichthyosawrus, as in many Lacertilians ; it is 
united with this bone in Sphenodon.” 
Nasals (na.).— The outline of these bones when viewed from above is triangular. 
They are elongate antero-posteriorly and form an acute angle where the two ele- 
ments pass beneath the overlapping premaxillee as shown by Owen” in I. camplyodon. 
The anterior sutural boundaries of these bones are best shown in the skull pertain- 
ing to specimen No. 603. Posteriorly and laterally the nasals are bent abruptly 
downward and form the outer surface of the skull in front of the orbit and above 
the nares. Anteriorly the outer surface is inclined less obliquely, gradually becom- 
ing convex as the nasals extend forward. Above, the nasals are widest at their pos- 
terior ends and in so far as one may judge from the damaged condition of this region 
they were somewhat concave transversely. Posteriorly the nasals united probably 
with the frontals and the prefrontals(?). The suture separating the nasal from the 
premaxillary begins at the upper anterior angle of the nasal opening and extends 
obliquely upward, forward and inward meeting its fellow medially at a point about 
one third the distance from the anterior to the posterior extremity of the skull. 
There is a small angular protuberance over the middle of the nares which I have 
not observed in other Ichthyosaurian skulls. The suture separating the nasals is 
plainly shown anteriorly in specimen No. 603. In the accompanying figure Pls. 
VIII. and IX., the anterior sutures have been drawn from that specimen. 
Lachrymal (la.}.—The lachrymal is a large subtriangular bone that joins the 
prefrontal (?) above and the jugal below to complete the anterior boundary of the 
orbit. The posterior border is concave. A spine-like prolongation extends back- 
ward beneath the eye and unites by suture with the anterior third of the jugal, this 
border more anteriorly meets the maxillary, terminating at the lower anterior border 
of the nasal opening. ‘The superior process presumably, meets the prefrontal and 
nasals above. he latter probably as in I. (zelandicus) quadriscissus sending down 
a small projection posterior to the narine opening to meet it. Anteriorly the oblique - 
superior border forms the lower boundary of the external nares. The facial surface 
29 Baur, G., lit. cit., p. 838. 
“Owen, R., ‘‘ British Cretaceous Reptiles,’’? Monograph, 1851. 
