138 GEOLOGY AND PALEONTOLOGY OF THE WEST INDIES. 



Pecten species, cf. Pecten oxygonum Sowerby. 



(Plate 10, Figure 7.) 

 IPecten oxygonum optimum Brown, Proc. Acad. Nat. Sci. Phila., p. 601, 1913. 



The following is a description of this species: 



Shell with many low, nearly obsolete ribs, each of which consists of 3 or 

 more radial threads with concentric, scabrous growth-lines. 



This is probably the species referred by Professor Brown to P. 

 oxygonum optimum Brown and Pilsbry. The single specimen in the 

 National Museum has very much lower ribs than are shown in the 

 figure of the Panamanian form. 



Locality. Willoughby Bay, Antigua, station 6881, Vaughan. 



Geological horizon. Oligocene. 



Figured specimen. U '. S. Nat. Mus. No. 167066. 



Pecten (.flSquipecten) perplexus, new species. 

 (Plate 8, Figures 8, 9, 10.) 



The following is a description of this species : 



Shell equivalve, equilateral, with 19 or 20 simple ribs with narrower inter- 

 spaces; minute sculpture of V-shaped spines arranged in longitudinal rows 

 on ribs and interspaces, those in the interspaces concave above and ventrally 

 inclined; submargins narrow, smooth or with a few radial threads; Camp- 

 tonectes striation present; ears large, subequal, with fine radial ribs, coarser 

 and nodose on right anterior ear; byssal notch one-half the length of the ear; 

 inner margin crenulated in accordance with the external ribbing. 



Alt., 28.5 mm.; lat., 26.5 mm. 



The spines are very easily eroded, leaving the shell either perfectly 

 smooth or with a single row of minute scales on the sides of the ribs. 



Localities. Crocus Bay, Anguilla, stations 6893, 6894, 6966, 6967, 

 6971, Vaughan. 



Geologic horizon. Oligocene. 



Types. U. S. Nat. Mus. No. 167076. 



Pecten (^quipecten) thetidis Sowerby. 

 (Plate 11, Figures 4, 5, 6.) 



Pecten thetidis Sowerby, Quart. Jour. Geol. Soc. London, vol. 6, p. 52, 1850. (Date of imprint, 



1849.) 

 Pecten thetidis Gabb, Jour. Acad. Nat. Sci. Phila., 2d ser., vol. 8, p. 346, plate 45, figs. 23, 



23 a, b, 1881. 



Pecten thetidis Gabb, Trans. Amer. Phil. Soc., new ser., vol. 15, p. 256, 1881. 

 Pecten (dZquipecten) thetidis Brown, Proc. Acad. Nat. Sci. Phila., p. 602, 1913. 

 Pecten (JZquipecten) thetidis Dall, Trans. Wagner Inst. Sci., vol. 3, p. 714, 1898. 

 Pecten (JEquipecten) thetidis Maury, Bull. Amer. Pal., vol. 5, p. 349, plate 60, fig. 6, 1917. 



The following is the original description of this species: 



"Testa orbicularis, tumida, radiatim costata, costarum marginibus quad- 

 ratis, ad utrumque latus squamuliferis, squamulis minutissimis, interstitiis 

 rugulosis; auribus inaequalibus, radiatim costatis, costellis squamulosis." 



