BAENID.. 



95 



restricted. On the other hand, the openings for the hind legs were large. It seems probable 

 that these turtles were accustomed to lying in the water in wait for passing victims and 

 leaping on them and seizing them. The hinder limbs were probably large and strong. 



Qusere alium, tua quern moveant miracula, dixit 

 Thescelus; utque manu jaculum fatale parabat 

 Mittere, in hoc h;esit signum de marmore gestu. 



Ovid, Met., v, 181. 



Thescelus insiliens sp. nov. 



Plates 24, 25. 



The basis ot this species is a specimen which was collected tor the American Museum ot 

 Natural History by Mr. Barnum Brown, in 1900, in the Laramie beds of Wyoming. The 

 locality more accurately stated is on Seven Mile Creek, about 5 miles north ot the Cheyenne 

 River, and about 40 miles west of the town of Edgemont, South Dakota. 



The specimen is a very complete one, presenting both the carapace and the plastron. The 

 carapace is in some parts, especially at the peripherals over the bridges, considerably fractured. 

 V erv tew parts are, however, missing, and the torm and the general structure can be deter- 

 mined. Unfortunately, both the bone and the matrix filling the interior are very friable. 



Traces of the sutures between the costals are present and have been indicated in the figures. 

 It has been found impossible to determine the boundaries of the neurals. Faint traces of the 

 sutures have lead to the provisional delimitation of the nuchal bone. The first peripherals are 

 probably correctly represented. It is believed also that the sutures between the various bones 

 of the plastron are correctly determined, where indicated definitely. The form and extent of 

 the epiplastra and entoplastron are conjectural, as no traces of the sutures can be made out. 



The form of this turtle is rather remarkable. Seen from above, the shell resembles that of 

 Caretta caretta. It is broad, not greatly elevated, with a median frontal excavation for the 

 neck, and narrowed behind. The plastron resembles greatly that of the species of Bahia. 

 It extends, however, far beyond the front of the carapace, while it fails equally as much to 

 reach the hinder border of the carapace. The bones are thin. 



The length of the carapace (plate 24) in the midline is 397 mm. The first peripherals 

 extend 21 mm. in front of the bottom of the anterior excavation; thus the total length is 418 mm. 

 The greatest breadth, across the middle, is also 397 mm. The height above the plastron is 

 140 mm., but in life it has evidently been somewhat greater. 



From the ends of the axis of greatest width the border of the carapace curves forward to 

 the anterior excavation. Passing backward from the axis referred to, the border is at first 

 very slightly concave to just behind the inguinal notches; then rather strongly convex for some 

 distance; then again rather strongly concave; at length convex to the midline behind. The 

 last concavity in the border would be over the hind legs, when extended backward. Beyond 

 the sinuosities mentioned, there are no notches, scallops, nor indentations in the tree borders ot 

 the carapace. The edge of the shell just behind the inguinal notches appears to have been 

 somewhat flared upward; but this appearance may be due to some distortion. 



In the hinder region of the carapace the peripherals are about 7 mm. thick and with acute 

 free borders. As the border of the carapace is followed forward, it becomes more obtuse. The 

 nuchal and the first peripherals are about 9 mm. thick. There are nowhere any carina; or 

 bosses on either the carapace or the plastron. 



The whole surface of the carapace is covered with a hard, enamel-like layer, like that of 

 Compsemys, Glyptops, and Trionyx. The ornamentation consists of raised dots and lines. 

 The latter are sometimes straight, sometimes bent, or brancht, or anastomosing. The general 

 effect is that ot shagreened leather. On each side of the sutures between the costals a band of 

 the surface is striated at right angles with the suture. It is from this striation, when present, 

 that the position of the sutures can be made out. Near the rear of the carapace there are such 

 indications of sutures as to justify the outlining of a suprapygal similar to that of Glyptops 

 pin atulus. 



The anterior portion of the carapace is unusually short, the abbreviation being at the 

 expense of the first costals, the anterior peripherals, and the nuchal. The form and position 

 of the latter are indicated provisionally, but there seems to be sufficient evidence to show that 



