72 AMERICAN PERMIAN VERTEBRATES 



Family Sphenacodontidae 



Marsh, Amer. Jour. Science, 411, May 3, 1878; Clepsydropidae Cope, Proc. 

 Amer. Phil. Soc, XVII, 529 (published May 8, fide Cope, as Paleonto- 

 logical Bulletin, No. 29). 



Carnivorous reptiles with high skull, anisodont teeth, and greatly 

 elongated dorsal spines. Cleithrum (always?) present; sacrum 

 with three vertebrae; pubes with greatly elongated, plate-like 

 expansion in front. Of moderate to large size. 



Under the assumption that S phenacodon has elongated dorsal 

 spines, of which, however, there is no evidence and much improb- 

 ability, the family name Clepsydropidae is quite synonymous 

 with Sphenacodontidae. If Sphenacodon has only moderately 

 elongated spines, and a general identity of its other characters with 

 Dimetrodon or Clepsydrops, it may perhaps require the modifica- 

 tion of the characters given above; or the family name may be 

 recognized as distinct. 



CLEPSYDROPS 

 Cope, Proc. Acad. Nat. Sciences, Philadelphia, 407, 1S75. 



The genotype specimen of this genus consists of a series of iso- 

 lated vertebral centra from the so-called Permian of Illinois. 

 In my opinion vertebral centra are wholly unreliable in this order 

 as generic types, to say nothing of species; they may be proven 

 eventually to belong to either of several related genera. How- 

 ever, Cope in 1878 referred a species from the Permian of Texas 

 to the same genus, which he called C. natalis, and it is from this 

 homotype that all the distinctive characters of the genus have so 

 far been derived. It is very probable, merely as a matter of 

 exclusion, that Cope correctly identified his Texas genus with 

 Clepsydrops, since we know that the limb bones associated with C. 

 natalis do closely agree with limb bones found associated with the 

 type, but not anatomically so, from the Illinois bone-bed. And here 

 is perhaps one of the best arguments against the strict rulings of 

 the international committee on nomenclature. If, fifty years hence, 



