HuTTON. — Oil a New Plesiosaur. 355 



the left side have been turned round so as to expose their 

 inner surfaces. Portions of four pectoral ribs are seen near 

 the right coracoid. Behind these vertebras are the pubes and 

 ischia, which have been but little displaced. Those on the left 

 side are nearly perfect, but those on the right side have lost 

 their outer margins. Behind the pelvic arch is the tail, the four- 

 teen vertebras of which have been split longitudinally in section, 

 so that no surface is seen. Anteriorly these vertebrae present 

 an indistinct mass, but the last seven on the slab show distinct 

 outlines. Here the specimen ends abruptly, but it is evident 

 that the tail must have been continued much further, as it 

 tapers but little. The transverse breadth of the last vertebral 

 centrum is 55mm., while the largest lumbar centrum has a 

 transverse breadth of only 65mm. These caudal vertebrae, 

 being in section, show that the articular surfaces of the centra 

 are more deeply concave than in most of the plesiosaurs ; and 

 the same can be ascertained for the trunk vertebrae by remov- 

 ing a portion of two of the centra. 



In the abdominal region, just in front of the pubes, there 

 are a number of rounded pebbles of quartz — about seventy-five 

 can be seen — varying in size up to 20mm. in diameter. As 

 similar pebbles are not found elsewhere in the rock containing 

 the saurian remains, it is evident that these have been 

 swallowed by the animal, probably to adjust the specific 

 gravity of its body with that of the water. 



The total length of the specimen is 5ft. 2|-in., of which the 

 tail occupies 1ft. Sin. The distance from the post-axial margin 

 of the coracoid to the pre-axial margin of the pubis is 1ft. 8in., 

 and the greatest antero-posterior length of the pelvic arch, 

 from the pre-axial margin of the pubis to the post-axial mar- 

 gin of the ischium, is 1ft. liu. The animal was about the 

 size of Plesiosaurus australis, to which it was referred by Sir 

 Julius von Haast ; but Sir James Hector pointed out that it 

 does not agree with that species either in the shape of the 

 ribs or in the form of the vertebral centra, and he considers 

 that "it must have been a very different animal. "'■= The 

 pelvic bones also differ much from those figured by Sir James 

 Hector. In the distinctly but moderately cupped articular 

 surfaces of the vertebral centra this specimen resembles P. 

 crassicostatus and P. hoodii alone of the described New Zea- 

 land sauropterygians ; but in both those species there is a 

 tubercle in the centre of the cup, which does not appear here, 

 and they both have the centra proportionately shorter than in 

 the present specimen. The proportions of length to breadth 

 of the vertebral centra resemble those of P. mackayi and 



* "On the Fossil Reptilia of New Zealand," Trans. N.Z. Inst., 

 vol. vi., p. 341. 



