G. B. Wieland — On Marine Turtles. 115 



especially in the lateral portion, indeed so thin as to suggest 

 the necessity for strengthening by overlapping dermal ossifica- 

 tions. The "anterior edge is strongly concave, being sharp, not 

 rounded, in the middle region. The nether or cervico-neural 

 articular process is prominent ; it takes the form of a heavy 

 trapezoidal ridge, longest in front, with a keel-like buttress 

 radiating from all four corners. 



The medial elements of Archelon are anomalous and require 

 discussion as well as description. At first sight one would 

 certainly say that there is a series of seven larger neurals fol- 

 lowing the broad thin nuchal, with four much smaller neurals 

 preceding a single pygal element and making eleven neurals 

 in all. On closer inspection, however, it is found that despite 

 the fact that the neural region of Protostega is of simple and 

 normal structure there is in Archelon a more complex arrange- 

 ment of parts than in any turtle thus far discovered — a condi- 

 tion moreover that has a more distinct bearing on the meaning 

 of the Dermochelan anatomy than any other thus far observed 

 in fossil turtles. 



In my original description I stated that " The medial plates 

 unite very imperfectly by means of loosely doubled interlock- 

 ing sutures and overlapping digitations grading into frequent 

 free spines [spine-like projections] posteriorly. These digita- 

 tions are mostly long, thin and ribbon-like, and produce a 

 junction quite different from the usual suture. In many cases 

 there is an appearance such as would result if the digitations 

 of the one plate had lain upon the surface of the adjoining 

 plate when it was in a plastic condition and thus raised rounded 

 ridging about their edges. The order of the digitations and 

 their size is rather regular." It was also explained that the 

 carapace was very thin on the midline and that at a break expos- 

 ing the section back of the sixth rib there were thin layerings. 

 And it should now be added that, bearing in mind that in the 

 mounted specimen the dorsal vertebrae remain articulated as 

 originally, I am, perhaps, censurable for not having the cara- 

 pace sawn through at the line say of the third, sixth and eighth 

 dorsal centra. However this may be it was not done, and, 

 awaiting further specimens, the type specimen in which all 

 details are certainly present must yield as its only quota of 

 new fact the superficial details. Indeed, were it not for the 

 accidental fact that back of the ninth medial element two 

 prepygal median elements are missing, and yet that there is 

 continuity of tiie carapace, it would likely escape us that two 

 layers of bone are present on the midline. At the point where 

 these elements have become disarticulated one can see that the 

 pleurals expand broadly beneath the median plates, but we 

 cannot tell to what extent they replace or crowd the neurals, 



