G. E. Wieland—On Marine Turtles. 211 



Art. XXI. — Notes on the Marine Turtle Archelon. L On 

 the Structure of the Carapace, II. Associated Fossils / by 

 G-. R. Wieland. 



In my first contribution on the osteology of the huge turtle 

 Archelon ischyros from the Fort Pierre Cretaceous of South 

 Dakota, I figured (Plate VI, Reference 6*) the last cervical 

 and first dorsal centra, together with the neurals and nine pairs 

 of ribs, as found articulated in their approximately natural 

 position, and associated with most of the other skeletal parts. 

 Since then I have secured much additional material from which 

 it will be possible to mount a quite complete skeleton. But as 

 this will require an amount of time and museum resources 

 equal, for instance, to that involved in the study or mounting 

 of any Dinosaur yet placed on exhibition, a considerable period 

 must elapse before any final contribution on this subject may 

 be made. Hence it may be of some immediate service if the 

 outline of the rib series in its entirety be given now, more 

 especially since this is found to be of unusual interest. 



Last autumn I secured near the Cheyenne River in South 

 Dakota, among other material, an important additional skele- 

 ton of Archelon, in which the first rib, that articulating with 

 the anterior end of the first dorsal centrum, is present. This 

 makes it possible to complete the rib series, as shown in the 

 accompanying text-figure. 



In the absence of much careful work by a preparateur it 

 would be difficult to indicate correctly the marginals in dotted 

 line, because of the digitate or strongly serrate character of 

 both the inner marginal borders, which vary much in different 

 portions of the series. The illustration of the completed Cara- 

 pace must for the present, therefore, remain in abeyance. 



Description. — The nuchal is a large and handsome T-shaped 

 element one meter in lateral width. I at one time provision- 

 ally regarded this bone as belonging to the plastron (7). This 

 view was, however, in the opinion of Capellini supported by 

 " neither embryological nor paleontological evidence " (2) ; Case 

 in a manuscript note kindly submitted to me likewise opposed 

 it. I am glad to find the complete evidence in accord with the 

 views of these eminent authorities. 



The neuralia are not of less area than in the Cheloninse, but 

 they are very thin, and are joined to each other and to the pleu- 

 ralia by strongly marked, more or less imperfectly interlocking, 

 sutural digitations. They are distinctly grooved on their median 



* For convenience the references are grouped at the end of the article. 



Am. Jour. Sci. — Fourth Series, Vol. XV, No. 87. — March, 1903. 

 15 



