KMYDIDJK. 



355 



Trachemys trulla sp. nov. 

 Plate 56, figs. 2-6; text-fig. 453. 



The type of this species is No. 31)34 of the American Museum of Natural History. It con- 

 sists ot portions of both epiplastra of a specimen which accompanied the type of Dr. Leidy's 

 Emys (Trachemys) petrolei; and was therefore obtained from the Pleistocene deposits of 

 Hardin County, Texas. Without additional materials it is not possible to determine with 

 exactitude the generic relations of the species, but the parts resemble most those of Trachemys 

 elegans, a present inhabitant of that region of the country. 



The bones forming the type are almost exactly the size of those of a specimen of T. elegans 

 \\ hose length ot carapace is 240 mm. From the latter it differs in having a much narrower lip, 

 that ol T. elegans being 59 mm. wide, that of T. trulla, 41 mm. wide. The lip of the latter 

 (plate 56, figs. 2, 3) is also of a somewhat different form. In T. elegans, seen from above, the 

 gulo-humeral sulci are directed outward and forward to the border of the epiplastral bones, 

 the lip projects rather abruptly, and it is subtruncated. In T. trulla each gulo-humeral sulcus, 



on the upper surface of the bone, runs directly forward, the lip 

 projects gradually from the border of the bone, and rounds for- 

 ward and inward to the midline. The free border of the lip of 

 T. elegans is usually, it not always, dentated; that of T. trulla is 

 smooth in outline. 



The lips ot both T. elegans and of T. trulla are excavated on 

 the upper surface so as to resemble somewhat the spout of a 

 pitcher. In T. trulla the sides of this spout descend more 

 abruptly than in the case of the observed specimen of T. elegans. 

 These sides rise each as a ridge some distance above the level of 

 the gulo-humeral sulcus and parallel with it. Anteriorly each ridge 

 descends into the free border of the lip. At the hinder end of each 

 ridge, at a lower level, is a deep pit. 



\t the midline on the upper surface the gular scutes extend 

 backward a distance of 15 mm. At the hinder end of the epi- 

 plastron the width of the humerals was about 15 mm. 



Seen from below, the middle of the lip descends little below 

 the general level of the epiplastral bones. The gulo-humeral sulci 

 are deeply imprest and they extended backward on the entoplas- 

 tron. The length ot the sulcus separating the gulars was 32 mm. 

 1 he suture between the two epiplastrals has a length ot 27 mm. 

 The thickness of the bones at the symphysis is 7 mm. The free 

 border of the epiplastron, where it joins the hyoplastron, is acute; 

 nil each side ot the gulo-humeral sulcus, thickened and rounded; 

 near the midline, again acute. 



With the bone described above are a right hyoplastron, a 

 right hypoplastron, and a left xiphiplastron which are supposed 

 to have belonged to the same species. These bones are represented by figs. 4, 5, and 6 of 

 plate 56. 



Text-fig. 453 is a restoration of the plastron, made up from the various bones that are 

 described above. 



This figure shows the relative dimensions of the bones and the positions of the scutes. 

 Fig. 4 of the plate cited presents a view of the upper surface of the hyoplastron, fig. 5 of the 

 hypoplastron, and fig. 6 of the xiphiplastron. The relative width of the beveled surfaces on 

 the upper side of these bones is displayed. All the free borders are acute, especially that of the 

 xiphiplastron. The notch at the rear of the hinder lobe was broad, but very shallow. The 

 hyoplastron is 7 mm. thick on the midline, at the middle of the length. The anterior end of 

 the hypoplastron, on the midline, is 7 mm. thick; but further backward becomes 10 mm. The 

 anterior end ot the xiphiplastron, at the summit of the bevel, is 7 mm. thick. The bones are 

 not sculptured. 



FlG. 453. Trachemys trulla. 

 Plastron restored from 

 bones figured on plate 56. 



