442 PROF. W. J. SOLLAS ON A NEW SPECIES OF PLESIOSAURUS 



8. The neural spines are inclined backwards as far as the 55th 

 vertebra ; past this up to the 57th they are inclined somewhat for- 

 wards ; but after this they again incline backwards to the end of the 

 yertebral series. 



9. The humerus and femur are nearly equal in length, the femur 

 being slightly the shorter. 



For the new species which these characters indicate, I propose 

 the name of Plesiosaurus Conyheari, as a tribute to that classic au- 

 thority who first made the existence and nature of Plesiosaurus 

 known to ns. This was sixty years ago ; and it is singular that up 

 to this date no one seems to have thought of calling some species of 

 Plesiosaurus after the author of the genus. 



Plesiosaurus Conyheari agrees closely with P. Eiheridgii in the 

 relative length of head and neck ; but if the length of the head be 

 compared in each with that of the whole cervico-dorsal series, a 

 marked difference is apparent ; thus in P. Eiheridgii the ratio is 

 12*5 : 100, in P. Conyheari 14*6 : 100. P. Conybearii further differs 

 from P. Eiheridgii in absolute size, being nearly twice as long ; it 

 also possesses a larger number of cervico-dorsal vertebras, P. Eihe- 

 ridgii having only 53, or 6 less than P. Conyheari. In this latter 

 character the new species more nearly agrees with P. homalospon- 

 dylus, each having 38 cervicals, while the latter has 22 and the 

 former 21 dorsal vertebras ; but P. Conyheari has a larger head 

 than P. homalospondylus. Both have the same length of neck ; but 

 P. homalospondylus has a longer dorsal series of vertebras (81 inches 

 in length). The length of its head relatively to that of the neck and 

 cervico-dorsal series is also much • less than in P. Conyheari, being 

 to the neck as 10*6 : 100, and to the cervico-dorsal series as 

 5-4 : 100. 



Detailed Description. 



The Skull (PI. XXIV. fig. 1).— This, which has been very thoroughly 

 freed from matrix, and is in an excellent state of preservation, pre- 

 sents us with that very exceptional character amongst Plesiosaurs, a 

 good profile. This is due to its having been compressed from side to 

 side, and not, as is more usual, depressed from above downwards. 

 Perhaps this indicates a difference in the original shape of the head. 

 The right side of the skull has slipped a little upwards above the left; 

 and some other displacements have occurred, but nothing like so great 

 as one would have expected if the present greatly compressed head 

 had originally been as broad from side to side as most Plesiosaur 

 heads evidently were. 



Posterior Aspect. — In the middle of the back of the skull is a con- 

 fused mass of bone comprising the axis and atlas vertebras, under 

 which the foramen magnum lies concealed. Inferior to this are the 

 posterior ends (articular e) of the rami of the lower jaws, bent to- 

 wards the middle line ; that on the right side is nearly perfect, 

 clearly not needing more than a quarter of an inch to complete it. 

 The articulare thins off rapidly behind its articulation with the qua- 



