274 0. P. Hay — Fossil Turtles in the Marsh Collection. 



The plastron is quite concave. The lip of the anterior lobe 

 projected boldly beyond the general border of the plastron and 

 beyond the front of the carapace. There is a considerable notch 

 in the posterior end of the plastron. The pectoral scutes are 

 about 55 mm wide at the midline ; the abdominals, 240 mm . 



This large and line species was found in the Titanotherium 

 beds of Indian Creek, Pennington County, South Dakota. It 

 is especially interesting because of its being the oldest known 

 species of the genus. Although so old, it appears to have been 

 as highly differentiated in all respects as are the modern forms 

 of the genus. 



Aspideretes beecheri sp. nov. 



Plate XVI. 



Trionyx foveatus Baur, G., Proc. Acad. Nat. Sci. Phila., 1891, p. 418 (not 

 Leidy). 



In the Marsh collection there is a fine specimen of a Trionychid 

 to which the above name is given. It was collected in the year 

 1889 by Professor J. B. Hatcher and Dr. C. E. Beecher, in the 

 Laramie beds of Converse County, Wyoming, on the east side 

 of Lance Creek. The specific name is given in honor of one 

 of the collectors, Dr. Beecher, whose untimely death has 

 wrought such injury to the science of paleontology. 



This specimen was examined by Dr. George Baur and iden- 

 tified by him as Leidy's Trionyx foveatus. The present 

 writer does not agree with this determination. Dr. Leidy's 

 species was based on rather scant material, but the ornamen- 

 tation of the costal bones is characteristic and' has led to the 

 identification of the species by Mr. L. M. Lambe (Geol. Surv. 

 Canada, Summ. Kept., 1901, p. 81, pis. i, ii ; Contr. Canad. 

 Palaeont., iii, 1902, p. 33, pi. i, figs. 1, 2) in finely preserved 

 and quite complete remains. The latter indicate a Trionychid 

 quite different from the one here described. 



The type of A. beecheri presents the limbs nearly complete, 

 a portion of the neck, the tail, the shoulder girdle, a large por- 

 tion of the carapace, and the whole of the plastron. 



The carapace had a length close to 325 mm and a width of 

 310 mm . At each end of the nuchal, the border has been some- 

 what excavated. The lateral margins are slightly sinuous, and 

 the posterior border has probably been slightly concave. 



The outer ends of the nuchal appear to have overlapped the 

 first costal. The nuchal has its whole upper surface covered 

 with a sculpture like that of the costals. There is a preneural 

 bone, whose anterior border has occupied a notch in the hinder 

 border of the nuchal. The author has elsewhere proposed 

 the name Aspideretes for the Trionychidse possessing a pre- 



