232 Mr. Williamson on the Distribution of 



(6.) This bed is apparently destitute of organic remains. 

 (c.) The following fossils have been found in this stratum, chiefly at 

 Clouahton : 



Rostellaria composita. 



Actseon glaber. 



Terebra vetusta. 



Phasianella cincta. 



Trochus. 



Avicula Braamhuriensis. 



Gervillia acuta. 

 Cucullea cancellata. 

 Astarte minima. 

 Cardita similis. 

 Pholadomya acuticostata. 

 Plesiosaurus. 



Of the Plesiosaurus, we have remains of only one animal, which was found 

 by my father near Scarborough, in 1825. 



To judge from the size of the humerus and femur, the creature w^as twelve 

 or fourteen feet long. The bones which have been obtained, consisting of 

 the humerus, femur, vertebrae, and phalanges, differ but little from those of 

 the Plesiosaurus Dolichodeirus of VVliitby and Dorsetshire. The humerus, 

 however, at its flattened extremity, expands equally on each side like the femur 

 of P. Dolichodeirus. Two detached teeth have been found, which, if they 

 really belonged to this animal, will prove a strong character in distinguishing 

 the species. They are about an inch in length, nearly smooth, and very 

 much resemble those of the crocodile. 



{d.) The nodules of ironstone sometimes contain specimens of Ammonites 

 Blagdeni. In this seam a mass of extraordinary bones was found, at the 

 White Nab, near Scarborough. Two of the bones agree in form with those 

 represented in fig. 4 and 5, of Mr. Mantell's " Illustrations of Tilgate Forest," 

 and supposed by him to be the metatarsal bones of the Iguanadon. The lon- 

 gitudinal circumference of the Scarborough specimens is 1 iJ- inches, and the 

 transverse IQJ- inches. The same mass contains also three bones, which re- 

 semble the humerus of an unknown Saurian, given in PI. 14, fig. 3 and 6, 

 of the same work. Their length is 14 inches ; the circumference about the 

 middle of the shaft, 8^ inches ; and around the condyle, 16 inches. There 

 are two other bones which are supposed to be tibias. They are ten inches 

 long; and their circumference at the superior extremity is 15i inches. The 

 circumference at the vertebral extremity of the fragment of a rib is 5 i^ inches, 

 and about the middle of the bone 6 inches. 



The same mass encloses also a singular bone, something resembling in 

 form the humerus of an Ichthyosaurus : the length of the supposed, cubital, 

 articulating extremity is S-^ inches, and the diameter 7 ; while the diameter of 

 the cylindric part, at four inches from the above extremity, is 3j^ inches. The 



