254 PALEONTOLOGY OF NEW JERSEY. 



specimens have been found." The type specimen came from Delaware. 

 The largest New Jersey example which I have seen is figured on the 

 plate as above. It bears all the characters of Dr. Morton's species, but is 

 somewhat compressed laterally, so as to give it rather less thickness, but it 

 is certainly not the young of ^. Delawarensis. On examining the type speci- 

 men of this latter species, the inner coils of which have been entirely 

 removed by decomposition, it is seen that up to a diameter of nearly 3 

 inches they would present much the same features as those possessed by 

 this specimen ; only that the transverse diameter has been "nearly or quite 

 an inch at the margin of the umbilicus, and that the sides are much more 

 convex, while the keeled character of the dorsum is much less conspicuous. 

 But it can readily be seen that all these features are liable to change with 

 the degree of lateral compression. The features of the septa appear to be 

 the same in two species, as will be seen by a comparison of the diagrams of 

 the small individual, which is enlarged to two diameters, with that of A. 

 Delawarensis, which is of mature size. The small individual from which 

 the figures above alluded to were made is the property of the Am. Mus. 

 Nat. Hist., and comes from Burlington County, New Jersey. The type of 

 A. Vanuxemi originally figured by Dr. Morton, when compared with the 

 inner coils of the large specimen of A. Delawarensis figured on our plate, 

 is not more than half as thick laterally where the dorso-ventral diameter is 

 the same; and the transverse ridges are finer, less elevated, and present an 

 entirely different feature, which compression would fail to produce on forms 

 like A. Delawarensis. 



Formation and localiti/ : Morton's type was from the Chesapeake and 

 Delaware Canal, and is from the lower part of the Lower Marls. The Bur- 

 lington County, New Jersey, specimens would be from the same geological 

 horizon. 



