MOUNT LAUREI^NAVESINK. 133 



formations the actual' number of Gastropods should be greater 

 than the table indicates, because of several undetermined forms, 

 but if all these species were included the proportion would not 

 nearly reach that shown by the Navesink fauna. 



The two species occurring in the Mount Laurel-Navesink 

 fauna, which may be taken as the most characteristic members 

 of the fauna, are Belemnitella americana and Terebratella plicata. 

 Neither of these occur in any of. the other faunas of the series. 

 The first of them has been detected in 19 of the 22 localities 

 which are recorded, and with a little search the species would, 

 doubtless, be found also in the other three. The second species 

 has been recognized in only 15 of the localities, but this, too, 

 would, doubtless, be found in most of the others were complete 

 collections available. These two species are totally different from 

 any of the forms which have preceded them in the region. They 

 could not have been derived through the processes of evolution 

 from any members of preceding faunas in New Jersey, and must 

 be considered as representatives of an immigrant element in the 

 fauna. Belemnitella americana occurs at widely distributed local- 

 ities in the southern States, but it is always a rare form, while 

 in New Jersey it is usually common and is frequently abundant. 

 Terebratella plicata, however, has not been recorded from any 

 of the localities of the Gulf-border region. The relationships of 

 B. americana are more close with the European B. mucronata 

 than with any other species ; in fact, it is doubtful whether- the 

 two should be considered as specifically distinct. In England and 

 France this species is highly characteristic of a horizon near the 

 summit of the Senonian. Terebratella plicata does not have so 

 close an ally in the European faunas, its closest relationship evi- 

 dently being with T. menardi Lam. of England and France. In 

 Europe this brachiopod occurs in the Upper Greensand, a hor- 

 izon considerably lower in the Upper Cretaceous than the Belem- 

 nitella mucronata zone. Still, the occurrence in European faunas 

 of a brachiopod so similar in form to this American shell, and 

 the entire absence of any related forms in other portions of 

 America, as well as the close relationship or identity of the species 

 of Belemnitella, strongly suggests a European origin for this 

 conspicuous immigrant element in the Belemnitella fauna of the 



