28 FOSSIL REPTILIA OF THE 



obvious that the natural form of the abdomen must have been deep and narrow^ like 

 that of the Water-Snakes [Hydrophides). 



The length of the last two abdominal vertebrae slightly decreases : a short, slender, 

 nearly straight and pointed pleurapophysis projects outwards from the diapophysis of 

 the last abdominal (lumbar) vertebra with which it has become anchylosed. The 

 pleurapophyses of the next two vertebrae are equally confluent with the diapophyses, 

 but are rather longer and much thicker than those of the preceding vertebra : they are 

 also slightly expanded and truncate at their ends ; they determine by these proportions 

 the ' sacral vertebrae,' which thus agree in number, as in general structure, in the 

 Bolichosaurus with those in existing Lacertians. 



Part of the bodies of the two sacral vertebrae has been destroyed, but evident traces 

 of the persistent cup-and-ball articulation between them remain. In the Scincoids 

 the bodies of the sacral vertebrae become anchylosed together. The extremities of the 

 sacral pleurapophyses come into contact in the Bolichosaurus, but do not coalesce : the 

 second sacral vertebra presents a ball to the first caudal, as in existing Lacertians, not 

 a cup, as in the modern Crocodilia. On the right side of the specimen the hinder half 

 of the iliac bone extends backwards, projecting freely a short way behind the second 

 sacral pleurapophysis, as in some modern Lacertians [Cyclodus, e. g.). On the left side 

 a part of the ilium is preserved, which extends to the acetabulum. A portion of the 

 expanded ischium is likewise preserved, and the distal half of the left femur extends 

 back in a right line from the position of the hip-joint. The length of the entire femur 

 could not have exceeded three centimeters, or fourteen lines ; it thus agrees in its 

 relative shortness with the humerus in fig. 1, 53, and accords with the idea that 

 the Bolichosaurus was more aquatic in its habits than the modern Lacertians, most of 

 which have longer proportional humeri and femora. The femur of the Bolichosaurus 

 had a medullary cavity. The under surface of the first two caudal vertebrae is im- 

 pressed by a median, longitudinal, shallow canal, bounded by two slight ridges, 

 diverging posteriorly in the second caudal to the tubercles (hypapophyses) that have 

 supported the haemal arch ; these tubercles are close to the posterior articulation. A 

 part of the spine of this haemal arch is preserved nearly in its true position. 



The foregoing comparisons show that all the general characters of the Lacertian 

 type of the vertebrate skeleton are presented by the Bolichosaurus ■ they are most 

 modified in the cervical region, where the Ophidian type is rather followed in the 

 number and size of the vertebrae, and in the size and shape of the ribs : a less decided 

 approach, but one still indicating an affinity to the Ophidians, is made by the unusual 

 length of the slender trunk, which includes, from the skull to the sacrum, not fewer 

 than fifty-seven vertebrae, and is not less than eighteen inches in length. The smallness 

 of the head accords with the long and slender proportions of the neck, and must have 

 added to the snake-like appearance of this early example of procoelian lizard. But the 

 complete and typically Lacertian organisation of the scapular and pelvic arches, and 



