MUSEUM OF COMPARATIVE ZOOLOGY. 97 



EXPLANATION OF PLATES. 



PLATE I. 



This plate gives a sketch map of the island of Martha's Vineyard, intended to 

 afford in mere outline sufficient indications as to the position of the Cretaceous 

 localities which have so far been determined. The principal locality where these 

 fossils are found is shown by the line indicating the position of the section given 

 at the bottom of the plate. From this point the fossils were obtained which are 

 mentioned in the text and figured in Plate II. The locality on Lagoon Pond lies 

 on the eastern face of that sheet of water from one third to one half a mile south 

 of the entrance to the pond. The fossils from this locality are extremely imper- 

 fect, and are found in occasional fragments of Cretaceous rock involved in a thick 

 section of drift. A third locality, where a single fragment of a fossil oyster was 

 observed, is on the southern part of the island of Chappaquiddick, which lies to 

 the east of Edgartown. 



At various points to the eastward of a line drawn from Great Tisbury Pond to 

 Lumbard's Cove the drift is frequently stained with ferruginous sandstone waste, 

 which is probably derived from Cretaceous deposits. It is possible that a portion 

 of the stratified rock deposits lying to the westward of the above mentioned line 

 may also be of Cretaceous age. 



For a further account of the geology and topography of this district, see my 

 Memoir on the Geology of the Island of Martha's Vineyard, in the Seventh An- 

 nual Report of the Director of the U. S. Geological Survey. 



PLATE n. 



Fig. 19, 20. Exogyra. Compare E. ostracina, Lam. 



