stinguishes this animal from all known quadrupeds; in the whole class of mammalia (some cetacea only excepted) the number of phalanges in the perfect and longest digits is restricted to three ; it is the same in most of the reptiles, but some saurians, e. g. the crocodile, exceed this number by one joint ; birds also have only five phalanges.
A majority of the cetacea appear to possess only three phalanges, but in some species the number is increased ; and the rorqual (a species of Balaena) and the Delphinus Delphis present as many as seven, (see Cuvier's Ossemens fossiles, Tome V., and Camper's Cetacea, PI. 44.) the nearest approximation to the number in the plesiosaurus, though less than the number in the posterior paddle of that animal by two joints.
Although all the other analogies of the fossil animal refer it to a class widely differing from the celacea, it is yet interesting to observe that in these instances, taken from beings of distinct general organization, the use for which nature intended this part, viz. natation, being the same, a similar modification has been superinduced on the usual structure of quadrupedal extremities.
On the whole, this part in the plesiosaurus presents a link between the usual structure and the still more complicated organization of the paddle in the ichthyosaurus ; the phalanges are flattened as in the turtle and other animals destined for natation ; and were doubtless in like manner covered by a common integument, and thus converted into a species of fins.
I shall conclude with some more general remarks. In its motion this animal must have resembled the turtle more than any other ; and the turtle also, as was before remarked, could we divest it of its shelly case, would present some slight approach in its general proportions to the plesiosaurus.
I shall leave to others more conversant than myself with the analogies of comparative anatomy, the inferences to which those particulars may lead concerning the habits of this singular animal.
That it was aquatic is evident from the form of its paddles ; that it was marine is almost equally so, from the remains with which it is universally associated ; that it may have occasionally visited the shore, the resemblance of its extremities to those of the turtle may lead us to conjecture ; its motion, however, must have been very awkward on land; its long neck must have