DERMATEMYDID^E. 



259 



Zygoramma microglypha Cope. 

 Fig. 322. 



Zygoramma microglypha, COPE, Proc. Amer. Philos. Soc., xn, 1871, p. 44; Vert.Cret. Form. West, 1875, 

 p. 263. HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 445. 



The remains described under the above name were found at Birmingham, New Jersey, 

 in the uppermost stratum of Cretaceous greensand. They consisted of the greater part of the 

 plastron and half of the carapace, with 4 peripheral bones, of an individual whose carapace 

 must have had a length of about 600 mm. A portion of this material has been recognized in 

 the Cope collection of reptiles, in the American Museum of Natural History, and this bears 

 the number 6129. Unfortunately, up to the present time, no bones of the plastron have been 

 found in the collection. No part of the species has hitherto been figured. 



The plastron is described as having a total length of 457 mm. According to Cope's 

 measurements, the length of the hyoplastron was 81 mm.; that of the hypoplastron, 145 mm.; 

 that of the xiphiplastron, 117 mm. The length of the hyoplastron was probably taken along 



themidline. The front of the plastron 

 was truncated. The width of the 

 entoplastron was 95 mm.; its length 

 something less; its thickness n.6mm. 

 The posterior border was truncated; 

 the anterior border, regularly convex. 

 The posterior plastral lobe was regu- 

 larly contracted, and rounded, and it 

 had a thin edge. Its width at the 

 hypoxiphiplastral suture was 220 

 mm.; the thickness at the midhne, 

 15.8 mm. 



The peripheral bones at the 

 bridges are said to have had a thick- 

 ened shoulder within, into which the 

 slender costal processes were received. 

 The free peripherals were of lighter 

 construction and somewhat everted. 

 Most of the bones of the carapace 

 that have been certainly identified are 

 here figured (fig. 322). These consist 

 of a portion of the first neural, the 

 third and the fourth neurals, the prox- 

 imal end of the first and third left cos- 

 tals, parts or wholes of the second, 

 third, fourth, and fifth right costals, 



FlG. 322. Zygoramma microglypha. 

 of type. X \. 



Portion of carapace 



c. p. I, c. p. 3, c. p. 5, costal plates; n. I, n. 3, n. 4, neural bones. 



and portions of other costals whose positions can not be determined. 



The first neural has a length of about 57 mm.; its width is 45 mm.; its thickness, 8 mm. 

 The third and the fourth have each a median length of 60 mm. and a maximum width of 

 37 mm. Each is excavated in front for the preceding neural. Each has a thickness, where 

 it joined the costal, of 10 mm. The first costal is 80 mm. wide; the second, 56 mm.; the third 

 59 mm. ; the fourth, 55 mm. On the lower side of the first there is the base of a strong rib- 

 head, and in front of this a rough articulation for the first rib. The rib-heads of the other 

 costals are very feebly developt. 



The sulci between the horny scutes are moderately distinct. The second vertebral had 

 a length close to 105 mm. and a width about equal to the length. The first vertebral must 

 have been considerably wider than the second. The third vertebral appears to have had a 

 length of 115 mm. and a width close to 95 mm. 



As in Z. striatula, the marginal scutes extend high up on the distal ends of the costal bones, 

 as may be seen from the figure. They pursue an irregular course. 



