118 
POSSIL REPTILIA OE THE 
platyodo7i ; the neural arch and spine have a less vertical, in proportion to the fore-and-aft, 
extent (PI. XXXI, fig. 6) than in Ich. communis or in Ich. tetmirostris. Eorty-five of 
these vertebrae may be counted between the occiput and the pelvis ; and as many 
beyond may be made out in the subject of fig. 4, PI. XXXI, as brings the number up to 
120, but the tail is incomplete. 
The length of the rostrum anterior to the orbit (PL XXXI, fig. 5) includes little 
more than three longitudinal diameters of that cavity ; it is thus relatively shorter than 
in Ich. platyodon, and it is relatively more slender than in Ich. mte^'medius. The mandible, 
however, does not partake of this proportion, but is nearly as deep and strong, rela- 
tively, as in Ich. platyodon (ib., fig. 2). The surangular (30) extends farther forward 
than the angular ( 31 ) ; both disappear in the usual pointed form. The nostril is divided 
from the maxillary by union of the premaxillary with the lacrymal. The pair of hyoid 
elements (cerato-hyals) are preserved in situ in the subject of fig. 5 ; they are cylindrical, 
almost straight, truncate at each end, which very slightly exceeds in thickness the rest of 
the bone. Each is about one fifth the length of the mandibular ramus. 
The coracoid (PI. XXXI, fig. 7) shows a deep anterior notch, with only a feeble 
concave outline at the corresponding part of the hind border of this bone. The clavicle 
is applied and suturally attached to the lower half of the fore border of the scapula. 
That border is nearly straight; the hinder one is concave through the backward pro- 
duction of the thickened lower end to contribute to the articular surface for the humerus. 
The anterior border of the radius and succeeding ossicle is emarginate. The chief 
phalanges of but three digits are preserved in the subject of PI. XXXI, fig. 4. The 
character of the pectoral fin of the present species is probably rightly indicated in the 
main ; and in such essentially tridactyle character Ichthyosaurus lonchiodon may agree 
with Ich. platyodon. 
The lower or distal ends of ischium and pubis seem to be equally expanded ; both 
bones are broader than the ilium. The ventral fin has been dislocated and bent back- 
ward close to the spine. The homotypal ossicles show the same emargination as in the 
pectoral fin. 
This species has hitherto been found only at Lyme Regis ; it appears to be a rarer 
Liassic Ichthyosaur than the three preceding ones. The skeleton above described was 
discovered by Miss Mary Aiming, to whom the discovery and extrication of many rare 
and interesting fossils of the Lias of this locality are due. 
/. Ichthyosaurus longifrons, Ow. PI. XXIII, figs. 1 — 5 ; PI. XXIV, fig. 1 ; PI. XXV, 
fig. 1 ; PI. XXVI, fig. 1 ; PI. XXVII, figs. 2—5. 
The characters of this species are those in which the subjects of the above plates and 
