74 



University of California. 



|VOL. 3 



such as would be advantageous iu inhalation by marine, air- 

 breathing 1 animals expanding the lungs considerably both at 

 the beginning and the end of a period of long-continued sub- 

 mergence. 



Short, robust ribs are seen in alexandrce close to the first 

 vertebra?, and similar ones are associated with the anterior 

 cervicals of osmonti. Toward the anterior dorsal region they 

 elongate rapidly. In the posterior dorsal region they are shorter 

 and heavier. Well developed diapophyses are present in the. 

 middle caudals in perrini (PI. 5, fig. 1), but no ribs from this 

 region have been uncovered . Contrary to the original description , 

 the rib- shaft is usually grooved on both anterior and posterior 

 sides (PI. 5, fig. 1.) This is most noticeable in the dorsal 

 ribs, on which the grooves may be very deep. On the fragments 

 of posterior dorsal ribs described with the type of the genus 

 the grooves are not well marked. Both grooves begin close to the 

 superior side of the shaft near the head and run out beyond the 

 middle of its length. Excepting the head, the proximal half of 

 the rib is narrow and rounded below. A broad, flat superior 

 surface is bounded by the anterior and posterior grooves. The 

 distal portion is almost circular in cross-section. The rib-head 

 is rather sharply twisted from the plane of the flattened prox- 

 imal portion of the shaft so that the upper portion is turned 

 backward. This is so pronounced in the middle dorsal region of 

 perrini that the plane of the rib-head is turned almost eighty 

 degrees from that of the shaft (PI. 7, fig. 4). 



Associated with the distal ends of the dorsal ribs of osmonti, 

 there are on one slab a large number of rib-like bodies very 

 much smaller than the true ribs. Though it has not been possi- 

 ble to make out their form definitely, they appear to vary in shape 

 somewhat, and almost certainly represent the several elements 

 of a series of abdominal ribs. In perrini also, a number of 

 fragments of very small ribs under the trunk may represent 

 abdominal ribs. 



Evidence of the existence of intercentra is found on the first 

 three known cervicals of osmonti (PI. 8, fig. 1), and the first four 

 of alexandroR. A prominent apophysis on the middle of the lower 

 side of the first cervical present in osmonti shows an anterior and 



