OPHTHALMOSAUEUS 61 



articulates with the femur proximally, the tibia anterinrly, aucl the intermedium and 

 fibulare distally. Of tlie proximal row of carpals, the tibiale {tib.) is the smallest, the 

 intermedium {int.) somewhat larger, and the fibulare {Jib.) larger still, the increase in 

 dimensions being mainly from side to side. As usual, the intermedium {int.) joins 

 both the tibia and fibula, its union with the former being the most extensive. The 

 distal row of tarsals also consists of three oval elements, the middle one being the 

 larger. In the most satisfactorily preserved hind paddle (text-fig. 41) there is a row of 

 three metatarsals ; of these the middle one alone has a phalangeal ossicle articulating 

 with it distally : probably there were other small nodules of bone representing phalanges 

 which have been lost. It is clear that the hind paddle consisted of three digits 

 (I.-III.) and has undergone extensive reduction. 



Ophthalmosaurus icenicus, Seeley. 



[Plate I. ; text-figs. 1-42.] 



1874. Oplithalmosaurus icenicus, H. G. Seeley, Quart. Journ. Geol. Soc. vol. xxx. pp. 696-707, 



pis. xlv. & xlvi. 



1889. „ ., R. Lydekker, Catal. Foss. Kept. British Museum, pt. ii. p. 9. 



1890. .. „ T?. Lydekker, op. cit. pt. iv. p. 267, fig. G2. 



1905-6. ,, „ C. W. Gilmore, Mem. (yarnegie Museum, vol. ii. pp. 125, 336. 



Ti/pe Specimen.— An imperfect skeleton (R. 2133) in the British Museum. 



This species was originally founded by Professor Seeley on a shoulder-girdle, which 

 occurred associated with the incomplete skull and skeleton of a single large individual 

 (PL I. figs. 11-15 ; text-figs. 4, 26, 33 C). 



In the present Catalogue it has been found impossible to distinguish more than 

 a single species. If only a few skeletons had been preserved several forms would 

 probably have been recognised and named, since taken individually some specimens 

 seem to difi"er very considerably from others. Moreover, if a single element of the 

 skeleton, say the quadrate, were taken as a means of determining the species, 

 several probably might have been distinguished, but these certainly would not corre- 

 spond with the specific divisions that might be founded on other elements. In 

 examining the immense collection made by Mr. Leeds and only in part catalogued 

 below, it becomes clear that these Ichthyosaurs vary considerably in details of the 

 structure of the various parts of the skeleton. The reasons for this extreme 

 variability seem to be, (1) diff"erences in the form of the bones resulting fi-om the 

 varying degree to which ossification has proceeded in a skeleton in which throughout 

 life much cartilage persisted ; (2) the mode of preservation of the bones and the 

 degree to which they have been distorted by earth-pressure ; (3) differences in the age 

 and sex of the individuals. It has therefore been thought best to refer all the 



