LIASSIC ICHTHYOSAURS. 71 



which may be termed ' abdominal.' The neural spines increase in length and fore-and- 

 aft diameter to beyond the middle of this region, and, by reason of their antero-posterior 

 breadth, they are in contact with each other. The fin-bend of the tail occurs at about 

 the seventy-sixth or eightieth vertebra. 



The di- and par-apophyses become confluent at or about the forty-sixth vertebra, and 

 such single ' transverse process,' or tubercle, disappears near the tail-bend. 



The ribs are slender, and become flattened and longitudinally grooved along their 

 distal halves. After the fortieth pair, or thereabouts, they become straight, short, 

 rounded, without the groove, and resemble mere ' transverse processes.' 



Three neural arches in the subject of fig. 1, Tab. XXVI, have been dislocated near the 

 bend of the tail. In these, the neurapophyses are short and confluent, with a trans- 

 versely broad, quadrate neural spine (Cut, fig. 5), the quadrature liL-ing due to an abrupt 

 truncation of the spine. 



Fig. !>. Frc. 6. 



Neural arch, front view. Caudal vertebra, side view. 



Nat. size. Nat. size. 



In the pinnigerous part of the column the neural arches (Cut, fig. C) 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, find 

 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 hsemapophyses (Cut, fig. 6) 

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

 bend. 



In the skull of Ic/iiJ/j/osarus intermedins the following characters may be noted. 



The under surface of the basioccipital is but slightly excavated anterior to the condyle, 

 and the ' foramen parietale ' is almost wholly in a raised part of the hind end of the inter- 



