148 Tfce American Naturalist [February, 



embryonic life. This fact does not, however, preclude the pos- 

 sibility that such a division may not have existed among the 

 ancestors of the Testudinata. As this order is very old, these ancestors 

 can only be looked for in the Permian and Triassic periods. Charac- 

 ters which belong to early geologic time, are frequently dropped out of 

 the embryonic record. Now in the Permian Eeptilia, some of which 

 are the ancestors of the Testudinata, the quadrate is a short element, 

 and is separated from the exoccipital and the opisthotic by a separate 

 bone which has been called mastoid and mastotympanic by Owen, 3 

 and which I have considered as part of the " squamosal " in the absence 

 of suture separating it from that element.* I think that such an ele- 

 ment exists in the Cotylosauria. The periotic bones in Empedias 5 

 audChilonyx are far removed from the elements which serve as sus- 

 penses of the quadrate bone, and are distinct from them in Chilonyx 

 at least. Owen (1. c.) thinks that a paroccipital has been fused with 

 the exoccipitals in Ptychosiagon (1. c), and in a position which shows 

 that it could not have been the opisthotic. The homologizing of one 

 or the other of these elements with the paroccipital of the Pythono- 

 morpha is too clearly among the possibilities to be negatived by any 

 evidence to the contrary yet brought forward by Dr. Baur. In fact 

 the origin of the opisthotic element as an ossification about the posterior 

 semicircular canal, renders it a priori probable that an osseous body at 

 a distance from that center, such as the distal part of the paroccipito- 

 opisthotic bones in the Testudinata, was originally distinct, and for 

 this element the name paroccipital is appropriate. 



2. The Exoccipital and Quadrate.— Dr. Baur again denies that the 

 exoccipital articulates with the quadrate in certain genera of Iguanidaj 

 and gives some figures of that region in the Conolophus subcridatus to 

 sustain his allegation. Unfortunately, though he seems to have taken 

 the elements apart, as I suggested that he do, he did not put them to- 

 gether in their original relation when he had them drawn. I now 

 give two drawings traced from the plate of the skull of the same spe- 

 cies given by Dr. Stein dachner. 6 As these plates represent exactly the 

 characters which I have observed and described in allied genera,*! re- 

 gard them as correct. It will be observed that there is a considerable 

 contact between the exoccipital and the quadrate. There is also con- 



3 Proceeds. Geolog. 8oc. London, 1859, p. 50. 



* Proceeds. Amer. A&soc. Adv. ScL, 1871, p. 207. 



'Proceeds. Amer. Plulos. Soc., 1-S8-",, p. 2M ; l.S'.»5,,,l. VIII, fig. 4, otic region 

 of Chilonyx. * ' ^ 



4 Die Schlangen u. Eidech,en der Galapagos Inseln, K. K. Zoolog. Botan. 

 Geae. Wien, 4to. 1876 ; pi. V. 



