BOTHREMYDID^E. 125 



The bones of the plastron (figs. 131, 132) are so fragmentary and contacts between the 

 pieces so rare that it is difficult to obtain measurements. The right epiplastron (fig. 131) is 

 represented by two fragments. One of these furnishes the symphysis. This is 36 mm. long 

 and the bone is 22 mm. thick. The hinder border was in contact with the entoplastron and is 

 1 8 mm. thick. The other fragment furnishes the hinder end of the epiplastron. There is 

 missing probably only a few millimeters of bone between the two pieces. The epiplastron, and 

 therefore the whole anterior lobe, was of a different form from what we see in Taphrosphys 

 strenuus. From the obtuse free border of the epiplastron to the entoplastron was nearly 

 70 mm. If the restoration here attempted approaches correctness the entoplastron must have 

 been at least 200 mm. wide. 



The hypoplastra at their inner anterior angles are 23 mm. thick. The upper layers of 

 the hyoplastra overlapt somewhat the hypoplastra. 



Of the hinder lobe (fig. 132) there are preserved several pieces. The restoration of this 

 lobe has been attempted and the recognized pieces of the lobe are represented by the stippled 

 areas. On the right side is seen a fragment which extends from near the inguinal notch to the 

 hypoxiphiplastral sulcus. The free border is rather obtuse, but becomes less so toward the 

 suture. The upper surface rises rapidly about 40 mm. and the thickness becomes 20 mm. On 

 the left side is a fragment presenting a portion of the hypoplastron and 110 mm. of the free 

 border of the xiphiplastron. The border may be called subacute. Three pieces of the right 

 xiphiplastron enable us to make out its characters; two of these form close contact and give us 

 the hinder angle and the notch. The other piece bears on its upper surface the eroded elevated 

 scar for articulation with the pubis. It appears to have the size and form seen in the species of 

 Taphrosphys. Just outside of this surface the bone is 17 mm. thick. 



The notch in the rear of the plastron had a width of about 185 mm. and a depth of about 

 80 mm. As the backwardly projecting angle of the xiphiplastron is approacht the bone 

 thickens and the free border becomes very obtuse. The thickness just outside the ischiadic 

 scar is 18 mm. The latter was elevated and rough, and apparently pear-shaped in outline. 



The anterior end of the epiplastron is ornamented with a close network of grooves, which 

 inclose spaces extremely irregular in size and form. On the hinder end of the bone the inclosed 

 areas are larger, more elongated, and parallel with the free border of the bone. The sculpture 

 of the rear of the plastron is similar to that just described. It is obscure on the central portions 

 of the plastron. The sulci of the plastron are obscure. On the epiplastron there is a gulo- 

 humeral sulcus beginning 38 mm. from the epiplastral symphysis and running backward 

 and a little outward to the suture with the entoplastron. 



This species is dedicated to Entellus, who, though old and lacking confidence, had endur- 

 ance and beat his younger opponent (Virgil's JEneid, book v). 



Genus NAIADOCHELYS nov. 



An imperfectly known genus of Pleurodira, having the plastral surface smooth, the hinder 

 lobe deeply and broadly notcht, and a large elevated ischial articular surface which extends to 

 the midline. 



Type: Naiadochelys tngravata Hay. 



This genus differs from Taphrosphys in having the lower surface of the plastron smooth, 

 instead of ornamented with longitudinal or anastomosing grooves, and in having a much more 

 extensive articular surface for the ischium. At present, only the hinder half of the xiphiplastron 

 is known. 



Naiadochelys ingravata sp. nov. 



Fig- '33- 



This species is based on a fragment furnishing about the hinder half of a left xiphiplastron. 

 It was collected in the year 1900, by Professor F. W. Putnam, having been brought to him by 

 Indians, at Chaco Canyon, New Mexico. The geological formation whence it was derived is 

 uncertain, but it was probably the Laramie, which is well developt in that region. The 

 specimen has been transferred from the department of anthropology of the American Museum 

 of Natural History to the department of vertebrate paleontology. The present number of the 

 specimen is 6078. The small amount of matrix yet clinging to specimen is a yellow sandstone. 



