49 



cnougli to excite the attention of naturalists. It is well known that the house 

 or boat oi llie tortoise or turtle is t'ornied hy the expansion of llie iisu;il 

 bones of the skeleton till they meet and unite, and thus l)ecome continuous. 

 'I^hus the lower shell is iornied of united ribs ol" tiie breast and of the 

 breast-bone, with bone deposited in the skin. In the same way. the roof 

 is formed by the union of the ribs with bone deposited in the skin. In 

 the very young tortoise, the ribs are separate as in otiier animals ; as they 

 grow older, they begin to expand at the upper side of the upper end, and 

 with increased age the expansion extends throughout the length. The 

 ribs first come in contact, where the process commences, and in the kuid- 

 tortoise they are united to the end. In the sea-turtle, the union ceases a little 

 aijove the ends. The fragments of the Protostega were seen by one of the 

 men projecting from a ledge of a low blutr. Their thinness and the distance 

 to which they were traced excited my curiosity, and I straightway attaciced 

 the bank with the pick. After several square feet of rock had been removed, 

 we cleared up the tloor, and found ourselves well repaid. Many long, slender 

 pieces of two inches in width lay upon the ledge. They were evidently ribs, 

 with the usual heads, but behind each head was a plate like the flattened 

 l)owl of a huge spoon, placed crosswise. Beneath these stretched two broad 

 plates, two feet in width, and no tliicker than binder's board. Tlie edges 

 were fingered, and the surface hard and smooth. All this was quite new 

 among fully-grown animals, and we at once determined that more ground must 

 be explored for further light. After picking away the bank, and carving the 

 soft rock, new masses of strange forms were disclosed. Some bones of a 

 large paddle were recognized, and a leg-bone. The shoulder-blade of a huge 

 tortoise came next, and further examination showed that we had stumbled on 

 'the burial-place of the largest species of sea-turtle yet known. The single 

 bones of the paddle were eight inches long, giving tlie spread of the expanded 

 flippers as consideral)ly over fifteen feet. But the ril)s were those of an ordinary 

 turtle just hatched, and the great plates represented the l)oiiy deposit in tlie 

 skin, which, commencing independently in modern turtles, unites with each 

 otiier at an early day. But it was incredible that the largest of known turtles 

 should be but just iiatched, and for this and other reasons it has been con- 

 cluded that this "ancient mariner" is (»ne of those forms not uncommon in 

 old days, whose incompleteness in some respects points to the truth of the 

 belief that animals have assumed their modern perfections l)y a process of 



growth from more simple beginnin>rs 

 7 c 



