4 HULKE, FOSSIL VERTEBRATE KRMAINS FROM SPITZBERGEN. 



rather narrow loug horse-shoe. Its vertical diameter, measured 

 at the articular surface, is 3,9 inches, and its maximum, hori- 

 zontal, transverse diameter is about 2,7 inclies. As all the 

 centra are slightly distorted, tliese measurements are only 

 approximately correct. The average antero-posterior diameter 

 is 1,4 inch. Upon the oiiter, or non-articular surface of the 

 third centrum in this series is an oblong rib-facet slightly 

 contracted at its middle, 1,2 inch long by 0,4 inch wide. Its 

 uppermost limit is 1,7 inch below the neurapophysial suture, 

 and from here it extends obliquely downwards towards the 

 anterior börder of the centrum. Its figure and its position 

 place this series of centra in the hinder part of the precaudal 

 or early in the caudal region of the spinal column. Their 

 articular surfaccs have the usmvl doubly-concave form. The 

 hollow is deep, but relatively to the whole area of the surface 

 its extent is small. For somo distance below the neural canal 

 the surface is nearly plane. 



The second series (II) consist of threc consecutive centra 

 much laterally compressed. Their antero-posterior diameters 

 nearly agree with those of series (I). A single rib-facet on 

 their outer surface, by its sliortness and its greater distance 

 from the neurapophysial suture, shows that these centra occu- 

 pied a posterior position in the spinal column to those of the 

 1st series. 



The dimensions of both these series of centra much sur- 

 pass those of centra of corresponding parts of the spinal 

 column of the types of I. communis, I. intermedius, I. lon- 

 chiodon, and also of all the loug-slender-snouted forms of 

 this genus in the British Museum. They equal those of I. 

 platyodon and some other large forms, which have been re- 

 ferred to this genus, but the proportions of the vertical and 

 horiziuital-transverse diameters of the articular faces distino-ujsh 

 the Spitzbergian centra from these. 



For this I propose the specific designation poJarin — 

 lehthyosaurus polaris. 



Ichthyosaurus Nordenskiöldii. 



Of the smaller species of Ichthyosaurus the best preserved 

 remains comprise two series of caudal vertebra^ detached from 

 tlu-ir uiiitrix; several othcrs disconnected, .scattered on shibs 



