114 FOSSIL REPTILIA OF THE 



In the pinnigerous part of the column the neural arches (Cut, fig. 6) gradually lose 

 breadth, gain length, and still more gradually lose height, the spine always predominating 

 in the fore-and-aft diameter ; the summit equals the centrum in that extent, and the neural 

 spines of contiguous vertebrae touch, but do not overlap. 



The vertical contour of the midpart of the centrum, above and below a more promi- 

 nent convex part, is slightly concave. The borders show the moderate convexity or 

 thickening, relating to the compressed characters of the pinnigerous caudals. 



The neurapophyses in the basicaudal region seem not to have coalesced above, and 

 the broad, laterally-impressed, and backwardly-produced part, simulates the half of a 

 truncated neural spine. The short, straight, and inferiorly-situated pleurapophyses con- 

 tinue to be developed to near the tail-bend. The shorter hseinapophyses (Cut, fig. 6) 

 are continued from the pinnigerous caudals to within a third part of the pointed tail-bend. 



In the skull of Ichthyosaurus intermedius the following characters may be noted. 



The under surface of the basioccipital is but slightly excavated anterior to the con- 

 dyle, and the ' foramen parietale ' is almost wholly in a raised part of the hind end of the 

 interfrontal suture. The maxillary is separated from the external nostril by the junction 

 of the premaxillary with the lacrymal. 



The sclerotic plates are from fifteen to seventeen in number. 



The surangular is deeper, and forms a larger proportion of the outer surface of the 

 hind half of the mandibular ramus than the angular. It terminates or disappears at the 

 usual point between the dentary and splenial, in advance of the angular ; it develops on 

 its upper border a small but well-marked coronoid angle bounding anteriorly the con- 

 cavity under the hind part of the orbit. Beneath this angle or process begins the neuro- 

 vascular groove, which extends, gradually shallowing, a short way forward. The splenial 

 element begins to show at the lower margin of the ramus about the mid-length of the 

 angular ; it unites with its fellow to form the hinder two thirds of the symphysis mandi- 

 bulse (PI. XXX, fig. 2, 32')- The articular piece is brought into view by its partial 

 dislocation backward in the right ramus of the subject of fig. 1, PI. XXX. 



The stem of the episternum equals in length one half of the cross-bar; in receding 

 therefrom it slightly expands and becomes flattened. In one young specimen a median 

 cleft extended a short way forward from the end. 



The clavicles are distinct, long, and less strong than in Ick. communis, feebly bent, 

 with the concavity behind and within, gradually narrowing to each end, and having a 

 sutural surface beneath and behind, some way along each end; the shorter one engrains 

 'with the episternal cross-bar, the longer one with the fore part of the scapula. Of this 

 bone the fore border is straight, the hind one concave through the backward production 

 of the humeral joint ; near this the outer surface is slightly excavated. In the coracoid 

 the humcro-scapular articulation is of less relative extent than in Ichthyosaurus communis. 

 The anterior notch is broader, but is as deep as the hinder one ; the intervening tract, or 

 neck, is relatively larger than in Ich jplatyodon or Ich. tenuirostris. 



