DLRMATEMYDIDiE. 



^37 



P> r. : 



type belongs to the Marsh collection in Yale University Museum and presents the nearly 

 complete shell. It was obtained in the upper bed of Cretaceous marl at Hornerstown, Mon- 

 mouth County, New Jersey, in 1872. It has been restored and fully described by Dr. G. R. 



Wieland, as cited in the synonymy. Dr. 

 Wieland's figures are employed in the pres- 

 ent work to illustrate the structure. 



The total length of the carapace (plate 

 35, fig. 1; text-fig. 296) in a straight line is 

 533 mm. The greatest width is 390 mm. 

 The form is that of an elongated oval, 

 broadest behind the middle, rounded in 

 front, more broadly rounded behind. Dr. 

 Wieland has called attention to a double 

 curvature along the sides. Possibly this 

 is due to slight distortion. From side to 

 side anteriorly the carapace is quite evenly 

 convex; posteriorly in the restoration it is 

 somewhat flattened. The hinder periph- 

 erals are flared somewhat upward, but the 

 front ones are not. The peripherals of the 

 free borders are thin and reduced to an 

 acute edge. In front of the axillary notch 

 the edges of the peripherals are somewhat 

 reverted, leaving a groove within the edges. 

 The nuchal bone is 70 mm. long on the 

 midline; 65 mm. wide on the free edge; 95 

 mm. where widest. There were 7 neurals, 

 of which all are present except the sixth. 

 Its form and dimensions are determinable 

 from the surrounding bones. The seventh 

 was not developt; the eighth is small. The 

 table below presents the dimensions of the 

 neurals. 



Most of the neurals are hexagonal, 

 with the broader end forward. The first 

 has the broader end behind; the second is octagonal. The absence of the seventh neural 

 permitted the seventh pair of costals to meet in the midline. Those of the eighth pair also 

 meet in the midline in front of the eighth neural. The single suprapygal is octagonal, 70 

 mm. long and no mm. wide. 



The peripherals are in general large. Their height, at right angles with the free border, 

 increases from the third to the ninth; the tenth has nearly the height of the ninth; the eleventh 

 is considerably smaller. The first peripheral extends along the free border 63 mm.; and 

 from this to the first costal, 65 mm. The second is slightly smaller in both dimensions. The 

 third occupies 50 mm. of the free border and is 65 mm. high. The ninth is 75 mm. along the 

 free edge and 103 mm. high. The eleventh occupies 62 mm. of the free border and rises 



toward the suprapygal 70 mm. The pygal measures 65 mm. 

 along the free edge and is 60 mm. high. 



The sulci are usually rather narrow and shallow. Those 

 nn the front are somewhat deeper and broader. The table on 

 page 238 gives the dimensions of the vertebral scutes. 



The costal and the marginal scutes are of unusual confor- 

 mation. The anterior marginals are mostly small; the lateral and 

 posterior remarkably large. As a result, most of the costals are 

 considerably reduced in area. The nuchal scute is 16 mm. long 

 and only 6 mm. wide. From this the marginals continue to rise 

 slowly above the free border to the hinder end of fourth, which 



FlG.296. Adocus punctatus. Carapaceof type. X0.18. 



c. p. i,c. p.2, c. p. 8, costal plates; in. s. l,m. s. 12, marginal scutes; 

 nu.p, nuchal plate; per, 2, per, 11, peripheral bones; py, 

 pygal ; spy, suprapygal ; n. 1, n. 6, neural bones. 



