MORPHOLOGICAL REVISION 



101 



below the proximal end the shaft is contracted and then spreads out in a wide, flat 

 distal end. This distal expansion is noticeable on the first four vertebrae, after 

 which the ribs are elongate and very slender. On the fourth vertebrae anterior to 

 the sacrum there is no face for a rib, so the last articulated rib probably occurred on 

 the twenty-first. 



Abdominal ribs: Williston detected a few very slender abdominal ribs just 

 anterior to the pelvis. They probably extended over the abdomen. 



Measurements. 



Type specimen of C. aguti, 4334 Am. Mus. mm 



Length of skull 67 



Width across quadrates 4.7 



Width of alveolar edge opposite center of orbit 25 



Interorbital width 20 



Length of ramus 61 



Greatest depth of ramus 11 



Length of humerus 34 



Width of distal end of humerus .... 25.5 



Specimen No. 4424 Am. Mus. mm 



Length of skull 70 



Breadth, approximate 60 



Length of humerus 35.5 



Breadth proximal end 12 



Breadth distal end 15.1 



Length of radius 19.5 



Length of pubis and ischium 35 



Genus LABIDOSAURUS Cope. (Plate 12.) 



Characteristic specimens: Nos. 4427 and 4876 Am. Mus. Nat. Hist., Nos. 641 

 and 642 University of Chicago. The mounted specimen in the Alte Akademie, 

 Munich. 



Labidosaurus is an abundant form in the upper part of the Texas Red Beds, 

 but the specimens are commonly very imperfect and covered by a refractory matrix; 

 recent discoveries, however, make the osteology of the genus fairly well known. 

 The following description is taken from several specimens, notably from the work 

 of Cope, Williston, Broili, and Case. 



The skull: The description of the skull is largely taken from Williston's recent 

 description of specimens Nos. 641 and 642 in the University of Chicago. 



"The skull is remarkable for its attenuated facial region, and for the beak-like 

 extension of the premaxillaries, terminating in the long, rake-like teeth. The nares, 

 situated nearly at the extremity of the rostrum, are semioval in shape, directed out- 

 ward. The face in front of the orbits is narrow, gently convex from side to side, 

 with nearly vertical sides and a gentle longitudinal convexity in the middle. The 

 orbits are a little longer than wide, their diameter a trifle greater than the interorbital 

 width. Posteriorly the skull is flattened in the middle above, and greatly expanded in 

 width, the expansion beginning near the back part of the orbits, the lateral margins 

 curving inward at the extreme posterior part. The large pineal foramen is situated 

 near the front part of the parietal bone, about midway between a line drawn through 

 the hind margins of the orbits and the hind margin of the skull in the middle line. 

 There is a pronounced emargination of the hind margin of the skull, extending the 

 width of the parietal bones. In well-preserved specimens the markings of the surface 

 of the skull are very distinct, consisting, for the most part, of round or oval pits 

 forming a reticulation, but not distinctly arranged in rows. In other specimens 

 these pits are less conspicuous, and the surface in some appears almost smooth. 



"The premaxillae are separated in several of the specimens in the museum. 

 They unite broadly above with the nasals, by a rounded border in front of the middle 

 of the nareal margins; and on the sides with the maxillae, below the nares. The two 

 bones together present a strong anterior convexity, with the alveolar border receding. 

 Each has three elongated, pointed, slightly recurved teeth, of which the innermost 

 is the largest, the outermost the smallest, less than half the length of the longest In 



