5<5o CRETACEOUS PALEONTOLOGY. 



Remarks. Whitfield has recognized two distinct species of 

 Crassatellites from the Manasquan marl, of about the same size 

 and very similar in form. Internal casts belonging to one or the 

 other of these species are not uncommon in the fauna of this bed 

 near Farmingdale and elsewhere, but it is practically impossible 

 to identify the two forms with any certainty. The most essential 

 difference between the two forms, judging from a careful study 

 of the descriptions and illustrations, together with at least a por- 

 tion of the typical specimens used by Whitfield, is to be found in 

 the character of the surface markings of the shells, C. littoralis 

 having rather strong, regular, approximate, concentric lines of 

 growth, while C. conradi has rather fine radiating costse. A 

 careful study of the specimens, however, seems to show without 

 doubt that these differences are only differences in the preserva- 

 tion of the shells, specimens having the actual surface intact being 

 marked with the concentric lines of growth, while those specimens 

 upon which the shell surface is exfoliated, exhibit the radiating 

 costae. Whitfield's illustration of C. littoralis showing the shell 

 surface (fig. 6), is a great deal restored, and on the specimen 

 itself, certain portions of which have been more or less deeply 

 exfoliated, the radiating costse are clearly vizible at several points. 

 On the other hand, one of the type specimens of C. conradi 

 (figs. 4-5), preserves a portion of the shell on the side opposite 

 to that which is illustrated, upon which fine radiating costae are 

 clearly seen, but upon careful examination it can be seen that 

 the actual shell surface has been nearly all removed and at those 

 points where it still remains it is concentrically marked; a por- 

 tion of the shell of this same specimen is also shown in the illus- 

 tration marked with concentric lines of growth, although in its 

 present condition the specimen has lost this portion of the shelL 

 From this it will be seen that the surface ornamentation of the 

 shells does not constitute a legitimate means of distinguishing the 

 two species. The differences in the outlines of the casts also 

 seem to be nonessential. Practically all specimens are more or 

 less imperfect about the margin, so that they appear to be of 

 various forms, and the angularity and prominence of the umbonal 

 ridge seems to be a variable character that cannot be depended 

 upon for specific value. From all these considerations, therefore, 



