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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 56. 



The carapace is subquadrangular in outline, broadly rounded behind 

 with a narrow median notch. The loss of the nuchal does not permit 

 a description of the anterior outlme of the shell. The median anterior 

 portions of the first pair of costals are deeply and broadly excavated, 

 as shown in figure 8, iudicating that a considerable portion of the 

 nuchal extended well posterior into the disk. The lack of sutural 

 edges along these borders would appear to show that the bony connec- 

 tion of the nuchal with the remamder of the disk was entirely with 

 the preneural, and that its lateral branches were probably free, as in 

 Aspideretes puercensis, at the most only overlapping the projecting 

 ribs extending from the first costal plates. 



Fig. 8.— Carapace of Aspideretes latus new species. Type. no. 8802, U.S.N.M. C. ), C. 8, 

 'costal bones one and eight; N. 1, S, S, 4, 5, 6, 7, S, neural bones one to eight. About one- 

 third NATURAL SIZE. 



In the complete sheU there were eight neurals; the first, however, 

 is missing in the type-specimen. It is the only Trionychid known to 

 the writer to have a fuU complement of neurals, as usually one and 

 often two posterior neurals are absent; thus six and seven being the 

 usual number of these bones. The eighth neural, though reduced in 

 size, lies partially between the eighth pair of costals and extends 

 nearly to the median posterior border. The second, third, and fourth 

 neurals are hexagonal, longer than wide, with the broad end posterior, 

 as in all Trionychids. The fifth is a paralellogram and only in contact 

 with the fifth pair of costals as in Aspideretes foveatus (Leidy). The 

 sixth and seventh are hexagonal with the broad end in front. The 



