126 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



"Beginning with the seventh, or possibly the eighth, caudal there is a 

 continuous series of fourteen or fifteen with chevrons, some of them, as 

 shown in the drawings, with the neural arches attached. It required a crit- 

 ical examination with a lens to distinguish the very small pleurocentra 

 of the posterior ones; that I did distinguish them I am quite certain. The 

 hypocentra are angular; the lower posterior part extended into stout chev- 

 rons, which were perforated near their base for the haemal canal. The distal 

 part of the tail was thin and high, possibly used as a rudder-like organ in life. 



"Ribs: Many of the ribs have been removed from their encrusting 

 matrix with but little or no injury; some of the posterior ones, because of 

 their extreme delicacy, could not be worked out completely. The first eight 

 pairs have broadly expanded proximal extremities, with a distinct separation, 

 save of the first pair, of the rounded and thickened capitulum from the more 

 elongated and thinner tubercle. The upper border is nearly straight or 

 gently convex on the proximal portion, convex beyond; for the three distal 

 fourths or more the shaft is slender, gently flattened, oval in cross-section, 

 and is curved downward. Beginning with the ninth rib, the proximal expan- 

 sion is much less, and there is no distinction into capitular and tubercular 

 articulations; the shaft is more slender. The ribs increase gradually in 

 length to the ninth and probably to the tenth. Beyond this they decrease 

 more rapidly in length. In the last two pairs, at least, they are reduced to 

 tuberculiform rudiments, ending pointedly, and are apparently coossified with 

 the diapophysis. 



" From the tenth to the eighteenth only the proximal parts were worked 

 out — that is, their precise lengths could not be determined. 



"Scapula coracoid: The scapula coracoid (plates 19-20) is a relatively 

 large bone, with no indications of sutural division into its supposed compo- 

 nent parts. The blade is moderately expanded above, gently concave on its 

 outer, convex on its inner, surface. Its upper border is a little convex longi- 

 tudinally, its edges sharply truncate for cartilage. The posterior border is 

 thickened to the beginning of the glenoid concavity; the corresponding 

 anterior border is thinned. 



"The posterior border divides to include the supraglenoid fossa, per- 

 forated at its bottom by the supraglenoid foramen. The outer border con- 

 tinues downward, and by a gentle curve backward to terminate in the oval 

 preglenoid facet, which looks downward, backward, and outward. The 

 inner margin, the thicker, extends downward, inward, and backward, with 

 an anterior curvature. In one specimen the end is angularly truncate, in 

 all probability for a small metacoracoid that was not ossified. In the others 

 it continues in a thin border back of the margin of the posterior glenoid facet. 

 This latter facet is near the lower part of the bone, an elongate concave 

 surface, with sharp margins posteriorly, and is opposed to the anterior facet 

 already described. Between these two facets and a little above them the 

 glenoid foramen pierces the bone obliquely backward to open on the inner 

 surface a little back of the border of the subscapular fossa, in which the 

 supracoracoid and the supraglenoid foramina both open. The lower ante- 

 rior part of the bone is thickened, with truncate edges, and is convex in 

 outline. The upper end of the cartilaginous border continues backward 

 as an angular thickening, nearly on a level with the upper border of the 

 preglenoid facet. The thickening extends as a ridge a short distance back- 

 ward. In much probability this ridge limits the upper border of the epi- 



