214 SAUROPTEKYGIA. 



length 0,027 (1-06 inches), height 0*028 (1-1 inches), 

 width 0,036 (1-4 inches). In the second the length of 

 the centrum is 0,072 (2*84 inches). The extremities of 

 two succeeding cervicals marked 4 and 5, together with 

 the second remaining centrum, closely resemble Nos. 

 25842-3 ; but it is probable that the centra corresponding 

 to those two specimens are missing from the series. These 

 early cervicals agree in all respects with the type cervicals 

 of P. helmerseni figured by Kiprijanoff in the ' Mem. Ac. 

 Imp. St. Petersbourg,' vol. xxx. art. 6, pis. viii. and xi. 

 In the cervical centrum marked 10 the length is 0,089 

 (3*5 inches), the height 0,066 (2-6 inches), and the width 

 0,092 (3*6 inches) : this specimen closely resembling the 

 slightly larger cervical from the Upper Chalk figured by 

 Schroder in the ' Jahrb. preuss. geol. Landesanstalt ' for 

 1884, pi. xv. fig. 1, as P. helmerseni. The dimensions of 

 a posterior cervical centrum marked No. 30 are :— length 

 0,106 (4-2 inches), height 0,109 (4-3 inches), width 0,152 

 (6-0 inches). In a " pectoral " (No. 33) the length is 

 0,102 (4-0 inches), height 0,117 (4-6 inches), width 

 0,152 (6-0 inches) ; this specimen closely resembles the 

 "pectoral" of a smaller individual figured by Schroder, 

 op. cit. pi. xv. fig. 2, as P. helmerseni. In one of the 

 dorsals the dimensions of the centrum are : — length 0,102 

 (4-0 inches), height 0,127 (5-0 inches), width 0-135 

 (5*3 inches). These dorsals cannot be distinguished from 

 the specimen from the Chalk of Sweden, figured by 

 Schroder, op. cit. pi. xvi. fig. 1, as the type of Pliosaurus (?) 

 gigas, the Plesiosaurian nature of the latter being at 

 once shown by the anchylosis of the arch to the centrum. 

 In a dorsal centrum of P. helmerseni figured by Kiprijanoff, 

 op. cit. pi. xii. fig. 2, the dimensions are : — length 0,099 

 (3-9 inches), height 0,114 (4-5 inches), width 0,140 

 (5-5 inches), or fully as large as those of the present 

 specimen. Gardner Collection. Purchased, 1876. 



28684. The centrum of a small immature dorsal vertebra pro- 

 visionally referred to this or the next species ; from the 

 Chalk of Dorsetshire. Length 0,043 (1*7 inches), height 

 0,056 (2-24 inches), width 0,061 (2-4 inches). Although 

 considerably smaller this specimen closely resembles the 

 dorsal figured by Kiprijanoff, op. cit. pi. vii. fig. 1. 



Mantell Collection. Purchased, 1853. 



