DERMATEMYDID&. 249 
the Adocidz. In 1891 (Proc. Acad. Nat. Sci. Phila., p- 429) Baur retains Agomphus in the 
Adocidee 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 by that of 4. tardus 
Wieland. 
KEY TO THE SPECIES OF AGOMPHUS. 
A‘. 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............. 0000 ccc ceccccccceceee. turgidus 
2. Plastron strongly convex transversely; costo-marginal sulci below middle of periph- 
Ela SHOP ta sree rr ces eT aie eee ee din Ge petrosus 
3. Like petrosus, but plastron not so convex ; costo-marginal sulci above middle of 
MSS ram mecca ate fates Tela a ests acres Yor. ane ce, exten, at hans! i clara cca nea chy acraatho ecoaceae te news ini eoenkls 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........... Bee etic ah woes Me etary ne oats tian ae pectoralts 
5. Entoplastron truncated behind; pectoro-abdominal sulcus nearer entoplastron than 
to hyohypoplastral suture............. .. firmus 
1. Entoplastron pointed behind; suture between hyoplastrals 0.35 of the hyohypo- 
MieeTStede Pe Core ism orata Maia ach auarateias A er oe ee ee ae masculinus 
A’. Early Tertiary species. 
r. With hinder lobe of plastron much narrowed behind. . . oxysternum 
Agomphus turgidus Cope. 
Plate 37, figs. 1-5; text-fig. 310. 
Emys turgidus, Corr, Ext. Batrach., Reptilia, Aves N. A., 1869, pp. 125, 127—?WiELanp, Amer. 
Jour. Sci. (4), XX, 1905, p. 440, fig. g, in part. 
Agomphus turgidus, Cope, Proc. Amer. Philos. Soc., x11, 1871, p. 46; Vert. Cret. Form. West, 1875, p. 
262.—Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 445. 
This species, the type of the genus A gomphus, 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 fourth 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 1481. 
The portion of the plastron (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 go 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 4. pectoralrs. The 
l 
