440 G. H. Wieland — Upper Cretaceous Turtles. 



Specimens 775 and 776* — (Figure 9). 



The characters of the plastron in the genus Agomphus are 

 shown in still further specific detail by the complementary 

 specimens 775 and 776 of the Marsh Collection, as represented 

 in the retouched photographic figure 9. These two specimens, 

 the parts of which are enumerated in the legend of figure 9, do 

 not necessarily pertain to the same species. In fact specimen 

 776 indicates a turtle with a slightly heavier plastron and 

 broader bridge than 775, although quite similar in all other 

 comparable respects. 



Specimen 776 probably belongs to A. {Emys) turgidus, 

 although we note that it may perchance be separated from this 

 form by the different outline of the humeral hornshields, and 

 from Adocus (or Agomphus) pectoralis by the relatively 

 larger plastral bridge. The bones, while unusually robust, do 

 not reach the great thickness seen in both A. tardus and A. 

 masculinus. 



It is furthermore to be observed that specimen 775 is dis- 

 tinguished from both the species just named as well as from 

 all other Adocidse so far as known, by the series of accessory 

 parallel growth lines of both the anterior and posterior sulci of 

 the femoral hornshields. This peculiarity, as distinctly shown 

 in figure 9, recalls the obverse condition of change from deep 

 sulci in the nuchal region to narrow line-like sulci on all the 

 rest of the carapace seen in Adocus punctatus. An imper- 

 fect accompanying hyoplastron however suggests proportions 

 similar to those of Adocus {JPleurosternum) pectoralis, which 

 we are fairly satisfied is an Agomphus. Were specimen 775 

 assigned to a new species, no one could say nay on the basis of 

 the material now known, but to do so could only be defended, 

 were no further examples likely to be yielded by the New 

 Jersey Cretaceous. 



While it is not therefore convenient to assign these specimens 

 to any of the half dozen known types, and much less so to pro- 

 pose a new species for No. 775, it is held that whoever is for- 

 tunate enough to discover additional new specimens illustrating 

 the doubtful points involved, will first be entitled to determine 

 these specific values. For the present it is therefore only 

 attempted so far as fairly practicable to make accessible the 

 features of Agomphid structure. JSlor do we consider that on 

 last analysis there is any essential difference between this 

 structural study and the more purely taxonomic point of view. 



* No. 775 is from the Cream Eidge Marl Co. 's pits, Hornerstown, Mon- 

 mouth Co., New Jersey. It was received at the Yale Museum in April, 1871. 

 No. 776 is doubtless from the same locality, but there is a discrepancy in the 

 Museum record, so that it is not positively known where this fossil is from. 



