4.16 The Rev. W. D. Conybeai'e on t?ie Discovei'y 



shaped processes, and three anterior dorsal with false ribs be- 

 fore the huniero-sternal portion. Since flexibility must evi- 

 dently be the end of this great multiplication of the joints, it 

 may perhaps excite surprise that the joints, instead of articu- 

 lating as in birds by cylindrical surfaces, should have their 

 contiguous faces nearly flat, which must have allowed a less 

 freedom of motion between each vertebra ; but it may be an- 

 swered, that the increased number of the joints compensated 

 for the stiffiiess of each. 



Dorsal Vertebrce. — I have nothing to add to my former re- 

 marks on this part of the column : the greater part of these, 

 in the splendid specimen from Lyme, are removed from their 

 place, and are scattered over the mass of shale in which they 

 are imbedded. In consequence of this accident, we are ad- 

 mitted to a full view of the ribs and sterno-costal arcs and 

 pelvis, which remain undisturbed. Fourteen large ribs may 

 be counted ; and twenty-one dorsal or lumbar vertebrae ap- 

 pear dispersed, though their exact original number cannot be 

 ascertained. The last of these lies over the pubis, and has, 

 close to it, a short false rib. 



Twenty-three caudal vertebrae are remaining ; and as about 

 three of the extreme ones appear to be wanting, we may pro- 

 bably assume this part at about twenty-six joints : the whole 

 vertebral column then will number about 90 joints ; viz. 35 cer- 

 vical, 6 anterior dorsal, 21 dorsal and lumbar, 2 sacral, and 

 about 26 caudal. The proportions of the whole of these parts 

 will stand nearly thus: taking the head as 1, the neck will be 

 as 5, the body as 4, and the tail as 3, the total length being, 

 as was before remarked, thirteen times that of the head. 



The chevron bones beneath the tail are finely exhibited ; 

 but this part, having been fully described in my former pa- 

 pers, suggests no new remarks, excepting that its shortness 

 must have prevented its being used, as in fishes, as an instru- 

 ment of impulsion in a forward direction, and that it was 

 therefore probably employed only as a rudder to steer the 

 animal by horizontal flexure, or by a sudden vertical stroke 

 to elevate or depress it while swimming through the water. 



The anterior sternal portion is greatly concealed by the 

 vertebrae and ribs lying over it; these might be carefully re- 

 moved and replaced, and the structure of this important part 

 ascertained. From several imperfect s})ecimens which I have 

 examined, it appears to have been complicated in its struc- 

 ture, and nearly to have resembled that of the Tnpinamhis. 



The posterior part of the sternum consists of a central bony 

 arc, crescent-shaped, and swelling in the middle ; to its horns 

 are applied two sterno-costal branches, which appear as usual 



to 



