OPTHALMOSAURUS PLEYDELLI. 11 



departure from the Plesiosaurian type has caused it to be assigned 

 to a new genus.* Similarly the departure of Oplithalmosaurus 

 from the Iclitliyosaurian type in the clavicle and propodial form of 

 the fore and hind-limbs induced Professor Seeley to remove 

 it to a separate genus. This change from the type appears to have 

 commenced after the Liassic period ; it has been found in the 

 Oxford Clay, the Kimmeridge Clay, and the cretaceous beds. 



Among a large mass of bones from the Kimmeridge clays of 

 Gillingham, kindly presented to the County Museum by Mr. 

 Freame, jun., I observed an Iclitliyopterygian humerus with three 

 facets at its distal end, two being the typical number. Feeling 

 sure it was a humerus of the new genus separated by Professor 

 Seeley from Ichthyosaurus in 1874 upon the evidence of a specimen 

 from the Oxford Clay of the neighbourhood of Peterborough, in 

 the collection of Mr. A. N. Leeds, of Eyebury, near that town, I 

 forwarded it to my eminent friend Mr. R. Lydekker, together with 

 a few other associated bones. The result of his examination will 

 be found towards the end of this memoir. I was glad to find my 

 opinion confirmed with the exception of a small humerus with 

 two facets, which I wrongly supposed to be the femur of the same 

 animal (the femur of an Ichthyosaurus is almost invariably much 

 smaller than the humerus). I was under the impression that the 

 hind-limb retained the typical number of two epipodial bones. Mr. 

 Lydekker decides it to be the humerus of a true Ichthyosaur, 

 which brings out the remarkable fact that the remains of two 

 animals, an Ichthyosaurus and an Ophthalmosaurus, were rolled 

 up together in the same clay-bed. 



Associated with the rest of the bones were portions of a massive 

 snout, the alveolar margins of which were unfortunately missing. 

 Five teeth of Ichthyosaurian character were found lying dis- 

 placed on the fragments of the snout ; they apparently 

 had fallen from their alveolar groove without violence. This 

 loose attachment of the teeth to the jaw might be a feature 



* See Vol. X. "Proceedings of Dorset Natural History and Antiquarian 

 Field Club," p. 171. 



