578 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



fine specimen of the E. orientalis from the Upper Missouri, as above 

 described. 



Posterior cervical vertebrae all furnished with a lateral angle, and all 

 much compressed; many anterior dorsals with sessile ribs; anterior 

 caudals strongly ribbed below E. platyurus. 



Posterior cervical vertebrse not compressed, and without lateral angle ; 

 median cervicals somewhat compressed ; few anterior dorsals with 

 sessile ribs; anterior caudals with weak angles below, 



E. SERPENTINUS. 



Posterior and median cervicals all depressed, and furnished with a lat- 

 eral angle E. orientalis. 



Elasmosaurus SERPENTINUS Copc, spccics nova. 



Established on one specimen in good preservation, which includes the fol- 

 lowing parts of the skeleton : — The entire vertebral column, with the ex- 

 ception of a few anterior cervical and distal caudal vertebrae ; the pec- 

 toral arch, with the clavicles a good deal broken; the greater part of 

 the anterior limb of one side; the greater part of the pelvic arch", with 

 a large part of both posterior limbs. 



The cervical series is estimated to cease where the first articulated 

 rib appears, which is attached to the first dorsal vertebra. The dorsal 

 vertebrae are reckoned to continue as far as the first centrum which 

 bears a chevron-bone, which is the first caudal. The numbers of the three 

 series which are preserved are: cervicals, 56; dorsals, 29; caudals, 18; 

 total, 103. It is probable that not more than two or three cervicals are 

 wanting, and perhaps ten caudals. This would give a total of 126 ver. 

 tebrse. In the Elasmosaurus platyurus first described, there were 103 

 vertebrae preserved, divided as follows : cervicals, 68 ; dorsals, 14 ; cau- 

 dals, 21. To these were to be added, cervicals, 4 ; dorsals, 10 ; caudals, 

 30 : totals, cervicals, 72 ; dorsals, 24; caudals, 40 : grand total, 136. The 

 column of the E. serpentinus presents then a greater number of dorsals 

 and a smaller number of cervicals ; as preserved, the latter are 56 to 

 68J, and as estimated 59 to 72. 



The forms of the cervicals are strikingly different from those char- 

 acteristic of the E. platyurus. This difference is seen in the centra, as the 

 flat,decurved,coossified diapophyses are similar to those of that species. 

 Throughout the entire series, the articular surfaces are broader than 

 high. This is especially marked in the anterior and posterior centra. 

 Near the middle of the series, the vertical diameter is but little less than 

 the transverse. In E. platyurus, the vertical and transverse diameters of 

 the anterior cervicals are nearly equal, but the superior diameter soon 

 becomes the greater, and continues so to near the posterior part of the 

 series. 



The difference between the two species is especially marked behind 

 the middle vertebrae, where the transverse diameter in the E. serpen- 



