308 PBOF. H. G. SEELET ON SIMILITUDES OF 



pressed, with subparallel sides, moderately elongated, and expanded 

 a little at the articular end, while it similarly carries the clavicle 

 along its anterior margin. The clavicle, however, is double, as 

 in some Ichthyosaurs, but otherwise not dissimilar, except that in 

 lizards its length is very variable, and sometimes, as in Scincus 

 and Iguana, it is compressed and widens from front to back. 

 The interclavicle of lizards is usually T-sbaped (though -f -shaped 

 in Scincus), and similar to that oi Ichthyosaurus, axct^t that most 

 lizards carry the cross bar behind the clavicles, though Polychrus 

 carries it below them as in Ichthyosaurus. The median bar, how- 

 ever, in lizards laps down the outside of the sternum, while in 

 Ichthyosaurus it binds the coracoids together. 



The pelvis is dissimilar ; for in lizards the ischium has a pos- 

 terior tuberosity, and the pubis an anterior tuberosity, the two 

 bones do not meet at the symphysis, while the ilium extends both 

 in front of and behind the acetabulum. 



The limbs offer no community of structure. The proximal end 

 of the femur in lizards has but one trochanter ; and that ia in 

 a line at right angles to the ovate compression of the head. 



§ 6. The Chameleon- Characters q/" Ichthyosaurus. 



The chameleon- skull offers no resemblance of importance to 

 Ichthyosaurus beyond such as are seen in the skulls of lizards, 

 except that the anterior nares are better defined andlatei'al, that 

 the orbit is relatively larger and has an osseous floor. The sutures, 

 however, are less well defined. 



The coracoid, but that it wants the anterior emargination, is like 

 that of Ichthyosaurus ; and the scapula, but that it is relatively 

 too long and has the anterior border concave, approximates to the 

 ichthyosaurian type. The chameleon pectoral arch differs in 

 wanting a clavicle and interclavicle, and in possessing a sternum. 

 The pelvis is very like that oi Ichthyosaurus, except that the ilium 

 is longer, and that the pubis and ischium do not meet at the sym- 

 physis. The pubis has the anterior margin straight, and differs 

 chiefly in being perforated by the obturator nerve. The ischium 

 differs chiefly in having a relatively greater antero-posterior extent 

 along the symphysis. 



§ 7. The Bhynchocephalian Characters of Ichthyosaurus. 



Hatteria agrees with Ichthyosaurus in having the median bones 

 which roof-in the skull all double ; it has a large foramen parie- 



