MOODIE: TURTLES AND PLESIOSAURS. 327 



SUMMARY. 



1. The grounds on which have been based the relationship 

 between the turtles and plesiosaurs are (1) the elongate char- 

 acter of the neck and tail claimed for certain turtle embryos ; 

 (2) the presence of epiphyses on the long bones; (3) the fu- 

 sion of the procoracoid to the scapula in the two groups; (4) 

 the possession of teeth in the two groups; (5) the girdles of 

 the plesiosaurs have been compared to the plastron of the tur- 

 tles; and (6) the similarity in form and habits of life. 



2. There are but eight segments in the neck of the turtle 

 embryos examined. There are from thirteen to seventy-six 

 cervical vertebrae in the plesiosaurs, according to Williston. 



3. There are no epiphyses on the long bones of either turtles 

 or plesiosaurs. The structures called "epiphyses" are the en- 

 dochondral cones found in all groups of the Sauropsida. 



4. The scapula of the turtle is a single element and the 

 procoracoid is not present. The method of formation of the 

 element is greatly different in the two groups. 



5. The elements of the pectoral and pelvic girdles in the 

 plesiosaurs are not homologous with the plastron of the turtles. 



6. The structure of the skull and the entire organization of 

 the animals is proof against relationship between the two 

 orders. 



7. The similarity of form and habits of life are due to 

 parallel evolution and adaptation for existence under similar 

 conditions. 



I am indebted to Dr. S. W. Williston for many valuable sug- 

 gestions and for several references. It was at his instance 

 that the study was first undertaken. 



