DERMATEMYDIDiE. 249 



the Adocidae. In 1891 (Proc. Acad. Nat. Sci. Phila., p. 429) Baur retains Agomphus in the 

 Vdocidx and gives as its distinguishing characters the narrow lobes of the plastron and the 

 shorter bridge. He states too that it has costiform processes which reach the second peripheral. 

 piercing the first. 



The general form of the shell of the species of this genus is indicated bv that of A. tardus 



fc> l c * 



Wieland. 



Key to the Species of Agomphus. 



//'. Upper Cretaceous species. 



a\ With the costo-peripheral sulci, so far as known, confined to the peripheral bones. 



1. Plastron nearly flat transversely; entoplastron broadly rounded behind; pectoro- 



abdominal sulcus much nearer the hyohypoplastral suture than to entoplastron; 

 costo-marginal sulci above middle of peripheral bones; costal border of peripherals 

 much thinner than maximum thickness turgidus 



2. Plastron strongly convex transversely; costo-marginal sulci below middle ot periph- 



erals petrosus 



^. Like petrosus, bur plastron not so convex; costo-marginal sulci above middle of 

 peripherals; costal border of peripherals not much thinner than maximum thick- 

 ness tardus 



4. Entoplastron pointed behind; pectoro-abdominal sulcus nearer hyohypoplastral 



suture than to entoplastron; suture between the hyoplastra 0.25 of the hyohypo- 

 plastral suture pectoralts 



5. Entoplastron truncated behind; pectoro-abdominal sulcus nearer entoplastron than 



to hyohypoplastral suture firmus 



<r. Costo-periphcral sulci of nth and 12th marginal scutes rising above the peripherals. 

 1. Entoplastron pointed behind; suture between hyoplastrals 0.35 of the hyohypo- 

 plastral suture masculinus 



A 2 . Early Tertiary species. 



1 . With hinder lobe of plastron much narrowed behind oxysternum 



Agomphus turgidus Cope. 

 Plate 37, figs. 1-5; text-fig. 310. 



Emys turgidus, Cope, Ext. Batrach., Reptilia, Aves N. A., 1869, pp. 125, 127. .'Wieland, Amer. 



Jour. Sci. (4), xx, 1905, p. 440, fig. 9, in part. 

 Agomphus turgidus, Cope, Proc. Amer. Philos. Soc, xn, 1871, p. 46; Vert. Cret. Form. West, 1875, P- 



262. Hay, Bibliog. and Cat. loss. Vert. N. A., 1902, p. 445. 



This species, the type of the genus Agomphus, is based on portions of the skeleton which 

 were obtained from the upper greensand bed of the Cretaceous of New Jersey. The materials 

 consist of both hyoplastra somewhat damaged; the entoplastron; the tourth neural; the 

 proximal ends of the third, fourth, fifth, and sixth costals of the left side, and of the third, fourth 

 and sixth of the right side; some fragments representing the distal ends of costals; and four 

 peripherals, one from the bridge. The specimen is now in the Cope collection in the American 

 Museum of Natural History, and bears the number 148 1. 



The portion of the plastron 1 plate 37, fig. 1) preserved has been considerably eroded. 

 The epiplastrals being gone, nothing is known regarding the form of the front of the plastron. 

 The front lobe had a width of 90 mm. at the base. The free border, as far as represented, is 

 thin and rounded in section, and a shallow groove runs parallel with it on the upper side. 

 Toward the midline the bone thickens rapidly, and at the hinder border of the entoplastron it 

 is 14 mm. thick. This increases to 17 mm. at the crossing of the median longitudinal and 

 transverse sutures. The entoplastron is rather pointed in front, broad and rounded behind. 

 It is slightly broader than long, thin in front (6 mm.) and thick behind (14 mm.). 



The transverse suture behind the hyoplastrals is somewhat irregular in direction. The 

 denticulations are fine, but there are some grooves and keels near the midline. 



Professor Cope states that only the longitudinal median sulcus is to be made out. Yet to 

 the present writer it seems clear that there is one which crosses the entoplastron, the humero- 

 pectoral, and another which crosses the hinder ends of the hyoplastrals, the pectoro-abdom- 

 inals. These are in exactly the positions of the corresponding sulci in A . pectorahs. The 



