PLESIOSATJEIDJE. 163 



The rugosity of the edges shows the immature condition 

 of this specimen. Sharp Collection. Purchased, 1876. 



R. 1378. An immature ulna or fibula probably belonging to this 

 species; from the Upper Lias, locality unknown. The 

 extreme length of this specimen, which is crushed flat, is 

 0,126 (5-0 inches). No history. 



Thaumatosaurus arcuatus (Owen 1 ). 



Syn. P/esiosaurus arcuatus, Owen 2 . 



Imperfectly known. Approaching in size to T. megacejohalus, but 

 with a relatively smaller skull and larger limb-bones, the humerus 

 being considerably larger than the femur, and the radius and ulna 

 much longer than the tibia and fibula. Coracoid elongated. Crowns 

 of teeth much curved, with the ridges on the inner concave surface 

 approximated and extending to the summits, and the carinae only 

 slightly developed. Cervical vertebras with a notch between the 

 pre- and postzygapophyses, and their centra relatively longer than 

 in T. cramptoni. 



Hah. Europe (England). 



2030*. The greater portion of the dentary bone of the mandible in a 

 (Fir/.) somewhat flattened condition ; from the Lower Lias, pro- 

 bably of Street, near Glastonbury, Somersetshire. One of 

 the types. Figured by Hawkins in his ' Memoirs on Ichthy- 

 osauri and Plesiosauri ' and ' Great Sea Dragons,' pi. xxvi., 

 and also by Buckland in his ' Geology and Mineralogy ' 

 (Bridgewater Treatise), pi. xix. figs. 3, 4 ; and described 

 by Owen in the ' Hep. Brit. Assoc' for 1839, p. 76. Most 

 of the teeth are wanting, but the traces of some remain in 

 the symphysis, and there are several replacing teeth in the 

 alveoli in this region. There are six enlarged tooth - 

 sockets; and the length of the ventral aspect of the sym- 

 physis is 0,082 (3-25). In the type mandible of T. mega- 

 cephalus, the corresponding dimension is 0,1.20 (4-7-5 

 inches) ; the two specimens agreeing so clearly in contour 

 that the difference in size forms the only apparent distinc- 

 tion. The present specimen closely resembles the man- 

 dible of T. indicus, but the dental alveoli have Becomo 

 flattened, and the diamond-shaped prominence on the oral 

 surface of the symphysis lias been split by pressure. 

 Buckland states that this specimen is from Lyme-Itegis. 



Haivlcins Collection. Purchased, 1834. 



1 Rep. Brit Assoc, for 1&3 ( J, p. 75 (l840).—Pleriosaurw. 2 Loc. cit. 



IE 2 



