Maryland Geological Survey 321 



Anne Arundel County, Maryland. The fauna of the Canal area is less 

 homogeneous in character than that of the Anne Arundel area, and one 

 or two of the faunal zones differentiated in New Jersey have been par- 

 tially recognized in it, although they are less sharply denned than in the 

 New Jersey area. In the immediate vicinity of Summit Bridge and at 

 Post 105 a fauna is represented analogous to that of the combined Mer- 

 chantville and Woodbury. It includes twenty-one or twenty-two species, 

 the most characteristic of which are : Liopistha alternata, Anchura 

 rostrata, Turritella delmar, Laxispira lumbricalis, Mortoniceras delawar- 

 ensis, Placenticeras placenta, and Scaphites hippocrepis. Turritella 

 delmar is known only from the environs of the type locality. Laxispira 

 lumbricalis, Anchura rostrata, Placenticeras placenta and Scaphites hip- 

 pocrepis are characteristic of the Merchantville of New Jersey and of the 

 Exogyra ponderosa zone of the South Atlantic and Gulf regions, while 

 Mortoniceras and Liopistha alternata are common not only to the Mer- 

 chantville of New Jersey but to the basal beds of the ponderosa zone 

 throughout the South Atlantic and Gulf states and to the analogous beds 

 of the Interior. However, the Summit Bridge fauna is probably the 

 equivalent not only of the Merchantville but of both the Merchantville 

 and the less definitely characterized Woodbury. Even within the limits 

 of New Jersey, Weller noticed that the differentiation between the two 

 horizons became increasingly difficult toward the south, and in Delaware 

 it is apparently obliterated. Both typical Merchantville forms, such as 

 Mortoniceras delawarensis, and typical Woodbury forms, such as Yoldia 

 longifrons, occur at a single locality, although the earlier types are 

 dominant. The Mortoniceras fauna is a relatively deep-water fauna and 

 notable for the absence of Exogyra and Gryphcea as well as the smaller 

 oysters. In this respect it stands in marked contrast to the fauna which 

 is most typically developed to the eastward on the Chesapeake and Dela- 

 ware Canal near Post 236. By far the most conspicuous elements in this 

 fauna, both from the point of view of abundance and also of proportions, 

 are the ponderous Ostreids. A number of species of the smaller bivalves 

 and univalves occur, but none of them are prolific, while the cephalopods 

 are very rare. The general aspect of the fauna is very similar to that of 



