MOUNT LAUREL^-NAVESINK. 135 



Cretaceous faunas of the Gulf-border region in America, where 

 it is more abundant, apparently, than in New Jersey. It may be 

 safely assumed that this species and some of its associates origi- 

 nated in this southern region in America and spread northward 

 to New Jersey, probably continuing eastward to where it is found 

 in the European faunas. The Gryphaea convexa, is perhaps not 

 distinct from the abundant European G. vesicularis Lam., and 

 the same or- closely allied forms occur commonly in the faunas of 

 the Gulf border region. It may have originated in the New 

 Jersey faunas from Europe or the east, although its appearance 

 in New Jersey in the Marshalltown associated with the southern 

 Exogyra ponderosa, before the appearance in the region of the 

 more clearly European Belemnitella, suggests that its origin also 

 was from the south. 



With the incomplete knowledge which we must necessarily 

 possess of most fossil faunas, it is difficult to analyze 'them 

 exactly into their component elements. Undoubtedly a consider- 

 able number of other species accompanied Belemnitella and Tere- 

 bratella in their migration from the east, and it may be assumed 

 that all the species characteristic of this fauna alone in New 

 Jersey and not known to occur elsewhere in America belong to 

 this class. Further faunal studies, however, especially in the 

 Gulf-border region may change the status of many of these 

 species, and it is not improbable that some molluscs which accom- 

 panied Belemnitella from the east spread into the southern region, 

 just as Belemnitella itself is known to have done. 



A third conspicuous element in the Mount Laurel-Navesink 

 fauna, distinct from the European Belemnitella and its associates, 

 and also from the southern Exogyra element, is the Cucullaea 

 fauna recurrent from the Merchantville and the Marshalltown. 

 The largest number of Mount Laurel-Navesink species common 

 to any other fauna of this New Jersey series, is found in the 

 Merchantville, and among these species are to be found such 

 highly characteristic forms as Axinea subaustralis and Cucullaea 

 antrosa, with an entire absence of the characteristic members of 

 the Lucina cretacea fauna of the Woodbury clay. 



The most characteristic species of the foreign immigration 



