W. O. Knight — Notes on the Genus Baptanodon. 77 



vidual characteristic had I not found it in at least three ani- 

 mals. The limb that I have been studying and have figured 

 differs from the one published by Marsh, inasmuch as the 

 abnormal number of digits do not appear until the phalanges 

 are reached, and then by a division of the third digit. This 

 information has been secured from a specimen in the matrix 

 and is absolutely reliable. The carpals, metacarpals and pha- 

 langes are coQipressed grooved cylinders, the most of which 

 have slightly concave surfaces. The grooves are ornamented 

 with tuberosities for muscular attachment. Along the margins 

 of the limb the cylinders have their exterior borders reduced 

 to quite thin edges. Any one finding the limb of a Baptan- 

 odon for the first time scattered about in the field would surely 



Figure 1. c— Transverse section of an interior carpal; d. — Terminal car- 

 pal ; E. — Marginal carpal. All reduced one-half. 



try to fit the ventral and dorsal surfaces of the metacarpals 

 together in trying to construct a digit. 



In comparing the limbs of Opthalmosaurus and Baptanodon 

 one should consider the following points : In Baptanodon the 

 humerus is about one-third the length of the arm ; it has a 

 twisted shaft which is greatly compressed. The distal facets 

 are all unequal in size and one of them is merely rudimentary, 

 besides they are elliptical in the plane of articulation. There 

 is also an abnormal number of digits, and the arm is much 

 more powerful and larger than found in Opthalmosaurus of 

 equal size. The indications are that Baptanodon was a remark- 

 able swimmer. 



Hind Limb. — The hind limbs in the collection are too frag- 

 mentary to admit of accurate determinations. The femora 

 examined all have two facets only. I was not satisfied with 



