142 SYSTEMATIC PALEONTOLOGY 



volving lines, and the small dislocated portion of the ribs are not of a 

 tubercular form; the aperture is longer and narrower." Conrad, 1843. 



" The shell is small, not exceeding 30 mm. in length, with rather 

 swollen whorls constricted narrowly above, much as in Pleuroinma of the 

 section Cymatosyrinx. The ribs are about 12 to the whorl and most 

 prominent at the periphery ; their posterior ends are constricted off 

 near the suture without any distinct groove or incised line; they are 

 strongly curved in front of the constriction; the surface has extremely 

 faint, obsolete spiral sculpture, only visible with the aid of a lens; the 

 pillar thin, simple, and twisted, rather short; the nucleus is conical, of 

 four smooth whorls like a small, very much elevated Calliostoma, except 

 that the whorls are rounded. A specimen 15 mm. long had ten whorls, 

 exclusive of the nucleus, and a maximum diameter of 4.75 mm." Dall, 

 1895. 



Length, 57 mm. ; diameter, 7 mm. 



Occurrence. — St. Mary's Formation. St. Mary's Eiver. 



Collections. — Maryland Geological Survey, Johns Hopkins I'niversity, 

 Philadelphia Academy of Natural Sciences, U. S. National Museum, 

 Wagner Free Institute of Science, Cornell University. 



Terebra (Acus) sincera Dall. 

 Plate XL, Fig. 9. 



Terebra {Acus) sincera Dall, 1895,Proc. U. S. Nat. Museum, vol. xviii [No. 1035], 

 p. 37. 



Description. — " Shell small, thin, acute-conic, fiat-whorled, with feeble 

 sculpture; whorls ten, without the nucleus; anterior half of the whorls, 

 with fine, feeble, spiral threading overrunning the ribs, posterior half 

 without spirals, but divided into two equal parts by a spiral groove visible 

 between the ribs; transverse sculpture of fine, low, even, narrow, 

 arched riblets, with wider interspaces, extending clear across the whorls ; 

 suture distinct, sutural band obscure, not swollen; aperture longer than 

 wide, outer lip thin, arched in harmony with the ribs ; pillar short, smooth, 

 or faintly excavated ; canal recurved, not contracted. Longitude, 22 ; 

 maximum diameter, 5 mm. 



" When superficially eroded the ribs are more prominent, as is the 

 succeeding whorl at the suture, and the whorls may have a slightly 

 turrited appearance." Dall, 1895. 



