Turritella from Buda and Georgetown Limestones 1 



MOLLUSCA 



GASTROPODA 



FAMILY TURRITELLIDAE 



Genus Turritella, Lamarck, 1799 



Turritella bybeei, h. sp. 

 Plate I, figures 1, 2 



Dimensions. Apical angle 22, sutural angle 6. 



Description. Shell large, thick, elevated, whorls four or 

 more in number, sides of whorls flat, suture well defined. 

 The aperture of the body whorl almost square, the base of 

 the whorl slopes at an angle of about 15 and is covered 

 with four or five nodular threads and striations. The orna- 

 mentation of the whorls consists of four rows of rounded 

 tubercles of which the first and third rows from the an- 

 terior side are the most prominent. Below the anterior 

 row are two nodular threads which almost disappear in the 

 upper portion of the spire. The anterior row of tubercles 

 is separated from the other three by a broad space. The 

 posterior row and the next one anteriorly are very close 

 together. The tubercles of the anterior row are elongated 

 instead of rounded as in the case of the other tubercles. 

 Very fine striations cover the whorls. 



Comparisons. Turritella bybeei differs from T. bravo- 

 ensis, Bose, 1 in the shape of the whorls and in the arrange- 

 ment of the ribs on the whorls. Our species has two nod- 

 ular threads in front of the anterior rib, whereas T. bravo- 

 ensis has a fine nodular rib bordering the anterior suture. 

 Between this fine rib and the anterior heavy rib is a band 

 greatly inclined toward the suture. This characteristic 

 does not appear in our species. 



, Institute Geologico de Mexico, Boletin 25, p. 149, pi. 31, figs. 

 8-9; pi. 32, figs. 1-2. 



