SYSTEMATIC REVISION 11 



Family DIADECTIDAE Cope. 



Cope, Am. Nat., vol. xiv, 1880, p. 304. 



Cope, Proc. Am. Phil. Soc, vol. xix, 1880, p. 45. Also Pal. Bull. 32. 



Cope, Proc. Am. Phil. Soc, vol. xx, 1882, p. 448. 



Cope, Proc. Am. Phil. Soc, vol. xxxiv, 1896, p. 439. 



Cope, Proc. Am. Phil. Soc, vol. xxxv, 1896, p. 130. 



Case, Jnl. Geol., vol. xm, 1905, p. 126. 



Original description: "American Naturalist," 1880: 



"The relations of the quadrate and zygomatic arches are as in the Theromorpha 

 generally. The pterygoids extend to the quadrates and the vomer bears teeth. 

 The brain case extends to between the orbits, and the lateral walls are uninterrupted 

 by fissures from this point to near the origin of the os quadratum. There is an enor- 

 mous frontoparietal foramen. The mode of connection with the atlas is peculiar. 

 There is a facet on each side of the foramen magnum, which then expands largely 

 below them. The bone which bounds it inferiorly presents on its posterior edge a 

 median concavity. On each side of this is a transverse cotylus, much like those of 

 an atlas which are applied to the occipital condyles of the Mammalia. They occupy 

 precisely the position of the mammalian condyles. The median point of their 

 upper border, which forms the floor of the foramen magnum, is produced in the 

 position occupied by the median occipital condyle of a reptile. From its position 

 between the cotyli, the section of this process is triangular. The element in which 

 the cotyli are excavated has the form of the mammalian basioccipital, and of the 

 reptilian sphenoid. It is not the batrachian parasphenoid. Its extreme external 

 border on each side where it joins a crest descending from the exoccipital, is exca- 

 vated by a circular fossa which looks outward." 



In 1882 Cope added (p. 448): 



"The sacrum consists of two vertebra; only, and is thoroughly united with the 

 pelvis by its transverse processes. The latter are decurved on the inner side of the 

 iliac bones, and the sutures which distinguish them from the latter and from each 

 other are not serrate. The inferior arch is robust, but very narrow anteroposteriorly. 

 The acetabulum is entire in every respect, so that it is probable that both pubis and 

 ischium are united indistinguishably in the arch. The pubis is perforated by the 

 usual internal femoral foramen. The posterior edge is grooved, and it might be 

 suspected that this marks the articulation of an ischium. The anterior edge is, 

 however, grooved in the same way, so that the appearance is rather the position of 

 muscular insertion. The spines of the sacral vertebrae are distinct, and have the 

 usual form seen in the Diadectes." 



In 1896 Cope gives the following table of characters and list of genera: 



"I. Posterior maxillary teeth transverse, depressed, molariform, the heel (external above, 



internal below) broad and flat. Skull without dermal or osseous sutures Empedias Cope. 

 II. Posterior maxillary teeth compressed, transverse, with non-molariform edge or apex, 

 except on wear. 

 a. Teeth with an external heel, besides the apical cusp. 



Cranial bones coossified; dermal scuta few or none Diadectes Cope. 



aa. Teeth with a cusp only. 



Adult cranium sutureless Bolbodon Cope. 



Cranium with osseous but no dermal sutures Plianerosaurus v. M. 



Cranium with both osseous and dermal sutures Chilonyx Cope." 



