484 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxii. 



Where the external ear was located is a puzzle. In all probability 

 there was an external tympanic closed membrane, as in the turtles. 

 The shortness of the stapes, if stapes this bone be — and there is no 

 other place in the skeleton where it can be located — must mean an 

 external surface close to the median line of the skull. There are no 

 incUcations of an otic foramen or notch anywhere about the quadrate 

 that I have discovered in this or other specimens of plesiosaurs. 

 Dollo has ventured the opinion, from the thickness of the preserved 

 cartilage about the external ear in certain mosasaurs, that they, or 

 certain types of them at least, were deep-sea divers, from the resem- 

 blance in the structure to that of the cetaceans. This ear cartilage is 

 very abundant and very thick in Platecar'pus and Tylosaurus, less so 

 in Clidastes. No calcified cartilage of any kind have I ever observed 

 anywhere in the skeletons of plesiosaurs, so that any inference as to 

 the habits of the plesiosaurs from its absence about the ear would not 

 be legitimate. 



Paddle. — A part of a paddle, evidently an anterior one, shown in 

 Plate XXXVI, was found in this specimen lying closely upon and 

 across the face of the skull. Not much information as to the generic 

 or specific characters of the form can be deduced from it, but I give, 

 nevertheless, a good photographic view of the specimen. The limbs 

 were evidently not of the slender type of the elasmosaurs, but whether 

 or not there was a duplication of the epipodials can not be determined. 



Vertehrse. — The remains of twelve cervical and six dorsal vertebrae 

 are preserved in the limestone matrix back of the skull. They agree 

 in all respects with the vertebrae described by me in the type speci- 

 men of BrachaucJienius lucasi, save in their slightly smaller size. 

 The cervical series is connected, as are also five of the dorsals, which 

 are curved forward reversed by the side of the cervicals. Doubtless 

 the specimen originally was composed of a large part, perhaps the 

 larger part of the skeleton, though only the single block containing 

 the skull and vertebrae and the attached paddle was secured by the 

 collector. At the angle of the vertebral series one or two may have 

 disappeared, but probably not more. I have every reason to believe 

 that the number of the cervicals is the same as in the type, namely, 

 13. The cervicals measure, in length, beginning with the axis: 25, 

 25, 25, 25, 28, 28, 30, 33, 35, 40, 40 mm. The dorsals preserved: 45, 

 50, 60, 60, 60 mm. The centra of the dorsals are smoothly rounded 

 on the under side, without excavations or vascular foramina, resem- 

 bling dinosaur vertebras so closely that it would be difficult to dis- 

 tinguish their centra if preserved singly. The cervical ribs are single- 

 headed, with not the least indication of division. 



The total length of the skull, with the missing premaxillary por- 

 tion estimated, is about 0.80 m., the width at the posterior part of 

 the orbits 0.35 m. The length of the type specimen is about 0.90 m.; 

 the width proportionally the same. 



