PLESTOSATJEID^:. 167 



dimensions is also noticed. The humerus has a length of 

 0,350 (13*7 inches), and a width at the distal extremity 

 of 0,178 (7*0 inches), and is thus absolutely smaller than 

 in T. arcuatus, while the skull is so much larger. The 

 ulna is relatively shorter and wider than in that species, 

 its length being 0/103 (4-1 inches) and its width 0,081 

 (3-2 inches), and the disproportion between this bone and 

 the fibula is much ]ess marked ; while the radius and tibia 

 are subequal in size. The cervical vertebrae and the pec- 

 toral girdle of this skeleton are of the general type of 

 T. arcuatus. 



Presented by the Trustees of the Bristol Museum. 



R. 1322. Slab showing the ventral aspect of a somewhat imperfect 

 omosternum, provisionally referred to this species ; from 

 the Lower Lias, locality unknown. This specimen closely 

 accords in general characters with the corresponding bone 

 of T. arcuatus, but is of somewhat larger dimensions, 

 although its apparent size has been somewhat increased 

 by the flattening to which its lateral borders have been 

 subjected. The diameter of the anterior border is about 

 0,178 (7 inches). Slight differences of contour as compared 

 with the above-mentioned specimen suggest reference to 

 the present rather than the preceding species. No history. 



Group B. — The arches of the cervical vertebras low and antero- 

 postcriorly elongated, with the longer axis of the zygapophyses 

 directed antero-posteriorly, and the pre- and postzygapophyses 

 separated by a long and shallow notch ; posterior border of 

 neural spine above centrum of succeeding vertebra. 



This group connects the preceding with Plesiosaurus, in which the 

 arches of the cervical vertebras have a similar structure. 



Thaumatosaarus zeilandicus (Phillips *), from the highest zone of 

 the Upper Lias, not improbably belongs to this group, since the ver- 

 tebras as described by Blake " arc longer than those of T. cramptoni. 

 The skull has a length of 1,065 (42 inches), being absolutely longer 

 than in T. cramploni, although tho length of the vertebral column 

 (10 feet) is less. There are said to be 25 cervical vertebrae, and 58 

 in the united cervical and dorsal scries. 



1 Rep. Yorks. Phil. Soc. for 1853, p. 7 (1854).— Plesiosaurus. See Blake in 

 Tate and Blake's 'Yorkshire Lias,' p. 249 (1870).— P. zetlandL 



3 In this description it appears that V. megacephalua has been confused with 

 Plesiosaurus macroceph alus. 



