10 PKOCEEDINGS OF THE NATIONAL, MUSEUM. vol.64. 



STRATIGRAPHIC SIGNIFICANCE OF ORTHAULAX CONOIDES. 



The specimens of Orthaulax conoides were obtained from a soft 

 clayey limestone that crops out in the area to be flooded by the pro- 

 posed dam on Eio Guajataca. Borings at the dam site show that 

 sandy and lignitic beds underlie this limestone. The sandy and 

 lignitic beds are about 150 meters below the bed where the specimens 

 of Orthaulax were collected. They resemble the rocks called " San 

 Sebastian," " Lares," and " Collazo shales " by different members 

 of the New York Academy of Sciences Scientific Survey of Porto 

 Rico and the Virgin Islands. These rocks are at the base of the 

 Tertiary section in the northwestern part of Porto Rico. As there 

 is no other field evidence indicating such beds at a higher horizon, 

 Mansfield believes that they are near the surface on the crest of an 

 unsuspected low anticlinal arch trending almost westward. 



Vaughan ^^ has recently corroborated Maury's -^ correlation of the 

 " San Sebastian," " Lares," and " Collazo shales " of the north side 

 of the island, and the " Guanica shaly limestone " of the south side, 

 with the middle Oligocene (Rupelian) Antigua formation of the 

 island of Antigua. 



The beds containing Orthaulax conoides are either an offshore 

 phase of the upper part of these beds or are the equivalent of the 

 overlying " Lares limestone," and are therefore considered of middle 

 Oligocene age. 



Evidence derived from other fossils is not very convincing. The 

 following additional mollusks were collected at the type locality of 

 Orthaulax conoides, station 1/139. Most of them are represented by 

 casts or impressions. 



Scaphander ? species. 



Turritella, species. 



Crcpidula ? species. 



Area, species. 



Barhatia, species. 



Clilamys (Aequipectcn), two species. 



Lima, species. 



EcMnocliama ? species. 



Cardium (Trachycardlum) , species. 



Teredo tubes. 



A coral from the same locality seems to be the same as a coral 

 collected by Hill at a locality 6.4 kilometers west of Lares, Porto 

 Rico (U.S.G.S. station 3191), and identified by Vaughan as Gijatho- 

 morpha antiguensis (Duncan) Vaughan variety. The coral from 

 station 1/139 is so poorly preserved, however, that positive identi- 

 fication has not yet been practicable. 



« Vaughan, T. W., Carnegie Inst. Washington Pub. 306. p. 118, 1921. 

 ^ Maury, C. J., New York Acad. Sci., Scientific Survey of Porto Rico and the Virgin 

 Islands, vol. 3, pt. 1, table opposite p. 4, Now York Acad. Sci., 1920. 



