BRYOZOAN FAUNA OF VINCENTOWN LIMESAND 3 



marl on formations of undoubted Upper Cretaceous age, now correlated with 

 the Eocene. The three formations and the overlying Shark River marl, the 

 Eocene age of which has not been questioned, are, on the evidence of common 

 fossil species, correlated approximately with the Pamunkey group (Eocene) of 

 Maryland. 



As intimated above, our studies of the Vincentown Bryozoa have 

 been almost entirely from the systematic and biologic standpoints, 

 so that our opinions as to the age of the formation are based solely 

 upon comparisons with the well-known Upper Cretaceous and early 

 Tertiary faunas of Europe. The Vincentown Bryozoa certainly show 

 close similarity to those of the Maastrichtian and Danian divisions 

 of Europe, with various genera and some identical species and little 

 relationship to the usual Tertiary faunas of either Europe or Amer- 

 ica. It is true that various characteristic species of the Vincentown 

 fauna are present in the Aquia formation in Maryland referred to 

 the base of the Eocene and likewise that the Clayton limestone at the 

 base of the Eocene (Midwayan) in the Gulf Coastal States contains 

 similar genera. It is evident that the much-discussed subject of the 

 Cretaceous-Tertiary boundary line is again in question. 



In spite of the abundant material available for study in the prep- 

 aration of this bulletin, certain biological details of some of the 

 species still remain unknown. The Vincentown limesand is usually 

 composed of unconsolidated sands (pi. 21), so that collecting consists 

 mainly in passing the loose material through a fine sieve and then 

 washing and assorting the myriads of specimens left behind. The 

 Vincentown, N.J., locality has furnished the greater part of our 

 material, but here the specimens are not so well preserved as at 

 Blackwoodstown, a locality now lost, from which a sample was col- 

 lected for the National Museum over half a century ago. The two 

 Delaware localities are represented by a few but most excellently pre- 

 served specimens furnished us by officials of the Maryland Geological 

 Survey. These three localities if rediscovered would undoubtedly 

 yield exquisite material for future studies. 



MEASUREMENTS 



Micrometric measurements for the determination of species of 

 Bryozoa were inaugurated by Smitt in 1872; they were adopted 

 in general for the Cyclostomata by Pergens in 1889, and for the 

 Cheilostomata by Canu in 1900. At the present time there is scarcely 

 an author who does not consider them indispensable. If not using 

 actual figures, the authors mention the scale of their illustrations. 

 Still another way of evaluation is to establish the number of cells 

 or apertures in a convenient unit. This number is often a specific 

 characteristic, and it adds to the value of the measurements and 

 simplifies the determination. 



