254 



FOSSIL TURTLES OF NORTH AMERICA. 



Agomphus pectoralis (Cope). 

 Plate 37, figs. 8, 9. 



Pleurosternum pectorale, COPE, Proc. Acad. Nat. Sci. Phila. 1868, p. 236; Cook's Geol. New Jersey, App. 



B, 1868 (1869), p. 734; Ext. Batrach., Reptilia, Aves N. A., 1869, p. 130. 

 Adocus pectoralis, COPE, Batrach., Reptilia, Aves N. A., 1869 (1870), pp. ii, 233, plate vii, fig. i; Proc. 



Amer. Philos. Soc., xi, 1870, pp. 296, 548; Proc. Amer. Philos. Soc., xn, 1871, p. 43; Vert. Cret. 



Form. West, 1875, p. 262. HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 444. 



The first mention of this species, under the name Pleurosternum pectorale, occurs in the 

 Proceedings of the Academy of Natural Science, Philadelphia, 1868, page 236, in the de- 

 scription of Agomphus petrosus. This mention may be regarded as sufficient to fix the date 

 of the species, altho the description is very brief and only incidental. Under the same name a 

 full description and a figure were publisht in 1869, in the author's work, Synopsis of the 

 Extinct Batrachia, Reptilia and Aves of North America. In a part of the same paper issued in 

 1870, the species was assigned to the genus Adocus. To the present writer the species appears 

 to belong to Agomphus. 



Agomphus pectoralis is up to the present time known to us by only the type specimen, 

 which consists of both hyoplastral bones (plate 37, figs. 8, 9). These are now in the Cope 

 collection, in the American Museum of Natural History, in New York, and they have the 

 catalog number 1478. The specimen was found in the upper bed of the Cretaceous green- 

 sand, near Medford, New Jersey. These hyoplastrals are complete, extending from the 

 sutures for the bridge peripherals of one side to those of the other. The width from side to 

 side is 146 mm. The free borders of the anterior lobe pass by a broad curve into the axillary 

 notch, making it difficult to determine accurately the width of the front lobe at the base. It 

 may be regarded as about 85 mm. 



The free borders of the epiplastrals are subacute, and from them the bone thickens 

 gradually to the median longitudinal suture. At the hinder angle of the entoplastron the 

 thickness is 15 mm.; at the hinder border of the hyoplastrals, in the midline, the thickness is 

 20 mm. Where these bones have joined the peripherals of the bridge, they are only 8 mm. thick. 



The hyoplastrals are deeply notcht for the reception of the entoplastron. This is pro- 

 longed further backward than in the other species of the genus. The axillary notches, too, are 

 very deep and narrow. Outside of each notch the hyoplastron sends upward and forward a 

 strong process, or buttress, against the carapace. Inwardly this forms a sharp crest. 



The dermal scutes of this species differ considerably from those of the species of Adocus. 

 Professor Cope thought that there had been a fusion of the humeral and the pectoral scutes, 

 and that the sulcus seen crossing the extreme anterior end of the left hyoplastron was the 

 posterior boundary of the gular scute. It seems more probable, however, that this sulcus 

 represents the posterior limit of the humeral. This interpretation throws the humero-pectoral 

 sulcus indeed far forward, but it is little more so than it is in Dermatemys mawii (Boulenger, 

 Cat. Chelonians, p. 28, fig. 8). On the outer ends of the hyoplastrals there are represented 

 three inframarginals. The axillary is small and, outside of the notch, extends well forward. 

 The second inframarginal is hexagonal and represents the hinder end of the axillary of Adocus 

 punctatus. The third inframarginal rested principally on the hypoplastron. In Alamosemys 

 substricta the arrangement is somewhat as in the species here described. The whole arrange- 

 ment of the scutes resembles closely that of Dermatemys mown, and there is little in the species 

 as known to exclude it from that genus. The species is here referred to the genus Agomphus 

 because of its close resemblance to A. turgidus. Only specific differences are observable. 



Agomphus firmus (Leidy). 



Emys firmus, LEIDY, Proc. Acad. Nat. Sci. Phila. 1856, p. 303; Smithson. Contrib. to Knowl., xiv, 1865, 



p. 106, plate xix, figs. 2, 3. COPE, Ext. Batrach., Reptilia, Aves N. A., 1869, pp. 126, 127. 



MAACK, Palasontographica, xvin, 1869, p. 277. 

 Adocus frmus, COPE, Proc. Acad. Nat. Sci. Phila. 1868, p. 235; Cook's Geol. New Jersey, 1868 (1869), 



p. 734; Proc. Amer. Philos. Soc., xi, 1870, p. 295. 

 Agomphus firmus, COPE, Proc. Amer. Philos. Soc., xn, 1871, p. 46; Vert. Cret. Form. West. 1875, p. 



262. HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 445. WIELAND, Amer. Jour. Sci. (4), 



xx, 1905, p. 443- 



