44 
Cope. ] [March 3,. 
observed in a former article. In A. syntheticus the sutures are a little 
coarser, and in A. agilis a further increase is seen, but with but little 
gomphosis. In A. pravus, according to Leidy, there is a little gomphosis, 
but how much is not ascertainable from his figure and description. In 
Homorophus insuetus, a stouter turtle, the gomphosis is very strong, 
especially in the longitudinal sutures, where the teeth are long and stout. 
In Zygoramma this coarseness of gomphosis reaches a maximum, being 
strong in all the sutures of the two species, except the anterior meso- 
sternal of 
ZYGORAMMA MICROGLYPHA, Cope, sp. nov. 
This large species is represented by the greater part of plastron and ° 
half of carapace, with four marginal bones, ‘of an individual from the 
New Jersey cretaceous, of two and a half feet in length. Its discovery is 
interesting as enabling me to refer this genus to the Adocidw without 
doubt, a point which the specimens of the original species, Z%. striatula,. 
Cope, left uncertain.* The episternal bone displays beautifully the wide 
intergular scutum separating the lateral reduced gulars. The postabdom- 
inal bone displays the swellings corresponding to the pubis and ischium. 
The pectoral dermal scuta advance medially on the posterior part of the 
mesosternal bone. These characters are those of Adocus. On the other 
hand there is not satisfactory indication of the intermarginal seuta, though 
they may exist, and the free marginal bones anterior to the bridge display 
the double articulation, by suture and gomphosis characteristic of Zygo- 
ramma. It might be here observed that it is possible that this structure 
will be found tu exist in + pecies at present referred to Adocus, A. agilis, 
for example, where the marginal bones are unknown. 
This species is one of those in which the mesosternal is received in the 
very open emargination of the hyosternals, a character indicating the 
breadth of the former, and seen in A. agilis and A. synitheticus. The 
bones are relatively thin, the marginals light and gently recurved. The 
anterior lobe of the plastron is truncate, the straight anterior margin 
grooved lengthwise. The posterior lobe is regularly contracted; and 
rounded, and with thin edge. The xiphisternal and hyosternal of the 
right side have each an oblique sutural union with the hyposternal of the 
“left. The mesosternal is broader than long, the posterior margin broadly 
truncate, the latero-posterior curved sigmoidally, the anterior regularly 
convéx. The episternal is but moderately thickened. The parts of thé 
hyposternals on the bridge are nearly in the plane of the rest of the plastron. 
The marginal bones near those of the bridge have a thickened shoulder 
above within, into which the slender costal processes are received : they 
thin out rapidly and are gently everted distally. More distal marginals 
are lighter and more everted. , 
The bones of the carapace include three vertebrals and numerous 
costals. The latter display very weak capitular processes, but in none are 
they entirely absent. Neither they nor the vertebrals are thickened. The 
* Proceed. Amer. Philos. Soc., 1870, 559. 
