Merriam.] 



Triassic 



Ichthyopterygia. 



77 



common with that element, though it shows some resemblance to 

 the scapula. As will be shown later, it does not come from the 

 pectoral arch at all, but probably belongs to the pel vie girdle. 

 The coracoid of alexandrce resembles that of Ichthyosaurus 

 communis somewhat, but is not so much expanded distally. In 

 osmonti it is still narrower. It is very thick and heavy in both 

 species, particularly so in osmonti, in which the distal end is 

 71 mm. thick, the greatest length of the bone being 150 mm. 



The scapula has a broad trianglar base (PI. 10, fig. 5), on 

 which is a large surface of articulation for the reception of the 

 humerus, and a much smaller one on the anterior side where it 

 rested against the coracoid. The thinner distal end is much 

 expanded, and turns downward and forward, forming a sharp 

 hook. It is quite different from that of any Ichthyopterygian 

 previously known to the writer, but is somewhat similar to that 

 of the Pythonomorpha. Its great distal expansion and anterior 

 nook are distinguishing characters. It is not so large as the 

 coracoid, but has about the some relative dimensions as in 

 Ichthyosaurus. 



A nearly perfect clavicle in the specimen of alexandrai is 

 a long and rather slender bone with a very deep groove on 

 the end next to the median line of the body. Along this 

 depression it probably fitted over the transverse bar of an 

 episternum. This latter bone is not well shown in any specimen, 

 but is possibly represented in aleooandrai by a fragment which 

 looks like the left end of the transverse bar. 



The complete pelvic arch is known only from perrini, where 

 all of the elements from both sides are preserved (PI. 5, 

 and PI. 6, fig. 1). In this specimen the bones referred to the 

 pelvic region and the posterior limbs lie immediately in front of 

 the first chevron-bearing caudals. That they have not wandered 

 back from the pectoral region is shown by the fact that a consid- 

 erable portion of an arch bone, probably a coracoid, much 

 larger than any of those in question, is present immediately 

 below the anterior dorsals; while the femurs and the whole six 

 elements of the pelvic girdle are accounted for. 



All three of the bones of the arch of perrini are so unlike 

 anything which the writer has found referred to Ichthyosaurus 



